(adds monitors may stay in Syria til Jan.22. para 13)
* Six civilians, five soldiers die, brigadier assassinated
* Arab foreign ministers to discuss Syria on Jan. 22
* More prisoners freed after Assad proclaims amnesty
By Alistair Lyon
BEIRUT, Jan 16 (Reuters) - Twelve people were killed on Monday in Syria, where a peace plan monitored by Arab observers has failed to douse a 10-month-old struggle between President Bashar al-Assad and his foes.
Arab foreign ministers meet on Sunday to discuss the future of the mission sent last month to check if Syria was abiding by the accord it accepted on Nov. 2. The mission ends on Thursday but the monitors may extend their stay to Jan. 22.
The Arab plan required Syria to halt the bloodshed, withdraw the military from cities, free detainees and hold a dialogue.
Hundreds of people have been reported killed in Syria even since the monitors deployed on Dec. 26 as pro-Assad forces try to crush peaceful protests and armed resistance to his rule.
Random gunfire by pro-Assad militiamen killed five people, including a woman, and wounded nine in the restive city of Homs, the British-based Syrian Observatory for Human Rights said. A sniper later shot dead a 16-year-old girl there, it added.
It said five soldiers were killed when they tried to change sides during a clash with rebels in the northwestern province of Idlib, adding that 15 soldiers had succeeded in defecting.
The state news agency SANA said an "armed terrorist group" had shot dead Brigadier-General Mohammed Abdul-Hamid al-Awad and wounded his driver in the countryside near Damascus.
U.N. Secretary-General Ban Ki-moon reiterated a call for Assad to "stop killing, and listen to his people".
During a visit to Abu Dhabi, he said: "I hope the U.N. Security Council handles Syria in a coherent manner and with a sense of gravity," but did not recommend any specific action.
"The casualties have reached such an unacceptable stage we cannot let the situation continue this way," Ban said.
The harsh response to the uprising by Assad's security forces has killed more than 5,000 people, by a U.N. count. The Syrian authorities say 2,000 members of the security forces have also been killed. The deaths of 32 civilians and soldiers were reported on Sunday.
The head of the Arab monitoring mission is due to report to an Arab League committee on Thursday before Arab foreign ministers gather on Sunday to consider their next step on Syria.
Adnan Khodeir, head of the monitoring mission's operations room, said the observers might stay in Syria until Jan. 22 while waiting for the outcome of the foreign ministers' meeting. Their mission officially ends on Thursday.
Qatar, which heads the committee, has suggested Arab troops step in, an idea that is anathema to Damascus and which Arab nations such as Iraq, Lebanon and Algeria are likely to oppose.
The League could refer Syria to the Security Council if it concludes that its own peace effort has failed.
RUSSIA, CHINA OPPOSE ACTION
The council has been paralysed so far because Russia and China oppose any resolution that could lead to U.N. sanctions or Western military action against Syria.
There is little Western appetite for any Libya-style intervention. The United States, the European Union, Turkey and the Arab League have announced economic sanctions against Syria.
On Sunday Assad proclaimed the latest of several amnesties for "crimes" committed during the uprising. Some prisoners were released the same day and more on Monday, activists said.
Mohamed Saleh, an activist in Homs, said about 185 people had been freed there, though some had been freed on bail and would still face trial. Many more were expected to be released.
Rami Abdelrahman, head of the Syrian Observatory, also said some activists had only been freed on bail. Many more were still held because the authorities had brought new, more serious charges against them that were not covered by the amnesty.
Kinan al-Shami, of the Syrian Revolution Coordination Union, said hundreds of detainees appeared to have been released, but they represented only a fraction of at least 40,000 people he said had been jailed without charge since March, many of whom have been held in secret police buildings or makeshift prisons.
The movement to end more than four decades of Assad family rule began with largely peaceful demonstrations, but after months of violence by the security forces, army deserters and insurgents started to fight back, prompting fears of civil war.
Assad, who retains the support of core military units, is backed by his own Alawite minority as well as some minority Christians and some majority Sunni Muslims who fear chaos, civil war and the rise of Islamist militancy if he is toppled.
The northern commercial city of Aleppo, like central parts of the capital Damascus, has mostly escaped the turmoil, but security forces stormed Aleppo University campus overnight in pursuit of students who staged an anti-Assad protest on Friday.
Activists said dozens of students were beaten in the raid, in which students belonging to a pro-Assad militia took part.
Aleppo residents say that big Sunni merchants in the city still support Assad and that the authorities have recruited Sunni tribesmen from the countryside to patrol the streets.
The president, 46, who appeared in public twice in as many days last week, is eager to show that his people love him.
SANA, the state news agency, reported on Sunday that a 10 km (six mile) long letter, which it billed as the world's longest, was being written and signed by Syrians across the country as a "message of loyalty to the homeland and its leader". (Additional reporting by Khaled Yacoub Oweis in Amman and Dominic Evans and Erika Solomon in Beirut; editing by Tim Pearce)