BEIRUT -- Fighting raged near a military base in Syria's north as a cease-fire in the bloody civil war was set begin Friday at dawn, activists said, illustrating the difficulty of enforcing even a limited truce coinciding with a Muslim holiday.

Elsewhere, violence appeared to die down, and thousands of protesters took advantage of the lull to mount some of the largest anti-regime demonstrations in months.

The truce, proposed by U.N.-Arab League envoy Lakhdar Brahimi and endorsed by the Security Council, is set for only the four days of the Eid al-Adha holiday, has no monitoring mechanism and no stated plans for its aftermath.

The first serious disruption involved a radical Islamic group, Jabhat al-Nusra, that rejected the cease-fire from the outset. The group clashed Friday with regime forces for control of a military base outside of a strategic town on the road to the northern city of Aleppo, according to the Britain-based Syrian Observatory for Human Rights, which relies on a network of activists.

Fierce fighting has been going on there for several days.

Opposition fighters seized Maaret al-Numan, which lies along the main highway between Aleppo and Damascus, earlier this month. Their presence has disrupted the ability of the Syrian army to send supplies and reinforcements to the northwest, where troops are bogged down in a stalemate with the rebels in Aleppo, Syria's largest city.

Activists said three people were killed in shelling of the Damascus suburb of Harasta and two people died as a result of sniper fire. There were no reports of clashes or protests at the time of the attacks, the Observatory said.

The Observatory said protesters rallied after holiday prayers in Aleppo, in central province of Homs and the city of Hama. Demonstrators also took to the streets in the suburbs of Damascus, and across the southern province of Deraa, where the uprising began. Three people were wounded when troops tried to disperse protesters in Deraa, the group said.

The demonstrations were reminiscent of the mass protests that ignited the civil war. In recent months, gatherings have been smaller, a result of a brutal crackdown by the Assad regime.

"It reminds me of the early days of the revolution, the days when people could go out and protest peacefully," said activist Khaled al-Shami, who is based in Damascus. Security was tight around the capital, and police forces erected additional checkpoints on main roads. In side streets, people performed prayers and protested freely, al-Shami said.

"It seems there is an attempt by both sides to abide by this truce, at least in Damascus," al-Shami said, adding that the truce was "a good thing that unfortunately will not last."

The latest fighting showed the complexity of the situation, with the badly fragmented opposition sending mixed signals about the truce, some endorsing it but others rejecting it as irrelevant.

President Bashar Assad's government accepted the truce but left significant loopholes, declaring it would respond to any rebel attack or attempts by foreign forces to intervene.

If the truce holds, it would be the first actual halt in 19 months of fighting that began with mass demonstrations but has transformed into a full-blown civil war with sectarian overtones and tens of thousands of dead.

Earlier attempts by mediators to bring about a cease-fire failed, though elements of both sides had accepted truce proposals.

Activists on the ground said the regime cannot be trusted because it has broken too many promises.

"The truce is a joke," said Mohammed Saeed, an Aleppo based activist, via Skype. "The regime that slaughters hundreds of its own people every day cannot be serious about a truce."

Saeed said the city was "relatively calm," despite shelling in several areas and clashes near the city's military airport that killed at least four people. The lull in fighting prompted hundreds to protest against the regime, he said, adding that there are marches in several neighborhoods, including in al-Shaar, Hanano and Bustan al-Qasr as well as in several suburbs of Aleppo.

Activists' videos that were posted online Friday showed, large groups of protesters waving rebel flags cheering, clapping and in some cases, dancing to revolutionary songs.

"May God curse your soul Hafez," they shouted in the Damascus suburb of Kfar Batna, in reference to Assad's father, the late Syrian president, Hafez Assad. They were also seen chanting, "Syria wants freedom" and "You will fall, Bashar."

Syria's state news agency said Assad attended holiday prayers in Al-Afram Mosque in Al-Muhajireen district of Damascus. The embattled president was shown briefly on TV, sitting on the mosque floor and praying. He was later seen smiling and shaking hands with worshippers.

Assad has rarely appeared in public during the uprising. He was last shown on state TV Oct. 6, when he laid a wreath to mark the anniversary of the outbreak of the 1973 Arab-Israel war.

More than 35,000 people have been killed, including more than 8,000 government troops, since the uprising against Assad began in March 2011, according to activists.

The Observatory said overnight clashes between troops and rebels took place in Homs, in Deir el-Zour in the country's east and in the city of Aleppo, the country's largest. At least seven people were killed in the fighting, including three rebels, the group said. Six soldiers were wounded.

On Thursday, rebels claimed major gains in the key battleground of Aleppo, Syria's commercial hub, pushing into predominantly Christian and Kurdish neighborhoods that had previously been held by pro-Assad forces in northern part of the city.

The short holiday cease-fire was all a divided international community could agree on after the failure of a more ambitious plan for an open-ended truce and political transition talks by Brahimi's predecessor, former U.N. chief Kofi Annan, in April.

Brahimi has not said what was supposed to happen after four days, an ominous sign, since Assad and opposition leaders disagree sharply on how to proceed. Assad refuses to resign, while some opposition leaders say his departure is a prerequisite for any political talks. The fragmented opposition factions disagree over whether to negotiate with Assad at all.

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Associated Press writer Zeina Karam in Beirut contributed to this report

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  • Syrian Regime

    Despite major defections and a July 18. explosion in Damascus that killed four top generals, including President Bashar Assad's brother-in-law, the regime's inner circle is still powerful and united against the opposition. Assad's inner circle includes his younger brother, Maher, who commands the forces in charge of protecting the capital. It also includes the heads of the four intelligence agencies playing a major role in the crackdown. Although regime forces lost parts of the northern city of Aleppo, Syria's largest, government troops still control most cities, while the opposition dominates large parts of the countryside. <em>Caption: This June 13, 2000, file photo shows Syrian President Bashar Assad, right, his brother Maher, center, and brother-in-law Major General Assef Shawkat, left. (AP Photo, File)</em>

  • Free Syrian Army

    The main rebel fighting force for more than a year, the Free Syrian Army includes lightly-armed volunteer militiamen and defectors from Assad's military. Its overall strength and structure is unclear, but tens of thousands are believed be loyal to the group. The rebels have control over some northern areas, allowing movement of fighters and supplies from Turkey and Lebanon. Anti-Assad forces have failed to maintain any strategic footholds in big cities, being driven back from key neighborhoods in Homs earlier this year and now apparently losing ground in the largest urban center, Aleppo. The battles also suggest only weak direction from central commanders - including Turkey-based Free Syrian Army leader Riad al-Asaad. <em>Caption: In this citizen journalism image provided by Shaam News Network SNN, taken on Sunday, Aug. 12, 2012, Free Syrian Army soldiers pose for a photograph, in Sarmada, Idlib province, northern Syria. (AP Photo/Shaam News Network, SNN)</em>

  • Syrian National Council

    Based in Istanbul, the SNC has emerged as the main political opposition to Assad and has pushed for international recognition as the legitimate representative of the uprising, despite rifts with other Syrian factions. The group also has been hit by internal feuds that have led some senior members to quit. The current leader, Abdelbaset Sieda, is a Swedish-based activist for Syria's minority Kurdish community. The SNC has gained support from many countries in the West and Arab world, but it has not galvanized international backing, and critics complain its senior leadership is made up mostly of exiles out of touch with their homeland. <em>Caption: The members of the Syrian National Council and its head Abdulbaset Sieda, center, arrive for a meeting with Turkey's Foreign Minister Ahmet Davutoglu in Ankara, Turkey, Monday, July 23, 2012.(AP Photo/Burhan Ozbilici)</em>

  • The National Coordination Committee for Democratic Change

    A rival to the SNC, the National Coordination Committee is led by opposition figures inside Syria, many of them former political prisoners. SNC members accuse the group of being far too lenient and willing to engage in dialogue with the regime. In turn, the National Coordination Committee accuses the SNC of being a front for Western powers and willing to open the door to the Muslim Brotherhood and other conservative Islamist factions. <em>Caption: Member of the National Coordination Committee for Democratic Change, Morhaf Mickael speaks during a meeting of Syrian opposition parties in Brussels on Sunday, June 24, 2012. (AP Photo/Virginia Mayo)</em>

  • International Alliances

    On Assad's side are traditional Shiite allies Iran and Lebanon's Hezbollah. <em>Caption: In this photo released by the Syrian official news agency SANA, Iran's Supreme National Security Council, Saeed Jalili, meets with Syrian President Bashar Assad in Damascus, Syria, Tuesday, Aug. 7, 2012. (AP Photo/SANA)</em>

  • International Alliances

    The regime also has important political cover from Russia and China, which have used their Security Council vetoes to prevent U.N. sanctions on Syria. <em>Caption: In this Jan. 25, 2005 file photo, Syrian President Bashar Assad, left, and Russian President Vladimir Putin shake hands during a signing ceremony in the Kremlin, Moscow. (AP Photo/Sergei Chirikov)</em>

  • International Alliances

    The rebels have built an array of regional support that includes the wealthy Gulf states - led by Iran rival Saudi Arabia - and neighboring Turkey, which offers key supply routes. The West also backs the rebel forces, but has so far opposed mobilizing international military support similar to the NATO-led airstrikes that helped topple Moammar Gadhafi's regime in Libya. <em>Caption: From left, Bahrain's Foreign Minister, Sheik Khalid bin AhmedI bin Mohammed al-Khalifa, Saudi Arabia's Foreign Minister Prince Saud al-Faisal, his Turkish counterpart Ahmet Davutoglu and United Arab Emirates' Sheikh Abdullah bin Zayed al-Nahayan seenduring a group photo during the Gulf Cooperation Council (GCC) Foreign ministers meeting in Istanbul, Turkey, Saturday, Jan. 28, 2012 (AP Photo)</em>

  • Foreign Fighters

    Syria has drawn foreign fighters just as other recent conflicts such as Iraq and Afghanistan. No credible count on them exists, but anecdotal evidence suggests foreigners are coming to fight Assad. Rebel commanders downplay the presence of foreign fighters, saying their cause is a purely Syrian uprising. Mohammed Idilbi, a Syrian activist based in Turkey, says foreign ranks include Libyans, Yemenis, Tunisians and Lebanese. On Saturday, Syria's official SANA news agency claimed four Libyans were among rebels killed in Aleppo. <em>Caption: In this Sept. 18, 2011 file photo, former rebel fighters celebrate as smoke rises from Bani Walid, Libya, at the northern gate of the town. (AP Photo/Alexandre Meneghini, File)</em>

  • Extremists

    U.S. officials and others worry that Syria could become a new foothold for insurgents inspired by al-Qaida. Assessing the degree of radical Islamic ideology in the civil war is impossible, but at least one group, the al-Nusra Front, has emerged and declared allegiance to the Free Syrian Army. Al-Nusra, or Victory, has claimed responsibility for several high profile attacks, including a double suicide bombing in March that killed 27 people in Damascus and the execution-style killing of a Syrian television presenter who was abducted in July. On Friday, U.S. intelligence officials said al-Qaida has advanced beyond isolated pockets in Syria and now is building a network of well-organized cells that could include several hundred militants. <em>Caption: This photo shows Al-Qaida's new leader Ayman al-Zawahiri in a still image from a web posting by al-Qaida's media arm, as-Sahab, Wednesday July 27, 2011. Al-Qaida's new leader has lauded protesters in Syria for seeking to topple the regime of President Bashar Assad. (AP Photo/IntelCenter) </em>