BAGHDAD — Extremists fired an explosive barrage Saturday into the capital's heavily protected Green Zone, targeting the heart of America's diplomatic and military mission in Iraq.

The U.S. military said there were no injuries from the early morning volley, which could be heard throughout downtown Baghdad.

The earth-jarring detonations, nearly 10 of them, even shook buildings across the Tigris River from the capital's fortified core, which houses the U.S. Embassy, military facilities and the Iraqi government.

The attack came shortly before Brig. Gen. Mike Milano, a top U.S. military official tasked with restoring security to Baghdad, said that nearly 80 percent of the capital's districts were now considered free of organized extremist activity.

The strikes were the most recent involving what Maj. Brad Leighton, a U.S. military spokesman, described as indirect fire _ the military's term for a rocket or mortar attack.

Similar volleys in the past week, including one against an Iraqi housing complex at Baghdad International Airport and its adjoining U.S. military base, killed 31 people, Milano said. He blamed the attacks on "al-Qaida and Iranian-backed special groups."

Special groups is a term usually reserved for Shiite extremist groups that have broken away from radical Shiite cleric Muqtada al-Sadr's Mahdi Army. Many are thought to be backed and trained by predominantly Shiite Iran.

In an upbeat assessment, Milano said a yearlong operation by the U.S. military and Iraqi security forces to make the capital safer had improved the situation.

According to Milano, when the operation began only 20 percent of Baghdad's 479 districts _ known as mahallas _ were relatively free of organized violence.

"Today 78 percent of the mahallas are considered free of organized extremist activities," said Milano, the deputy commanding general of the U.S. Army's 4th Infantry Division.

He added that since June 2007 there had been a 75 percent decrease in attacks in Baghdad, a 90 percent decrease in civilian casualties and an 85 percent decrease in murders.

"All these indicate to me an improved security situation," he said.

Baghdad, however, remains far from safe. The Iraqi military indefinitely banned all motorcycles, bicycles and hand-pushed and horse-drawn carts from the city's streets, a military spokesman said Saturday.

Although the reason for the motorcycle and bicycle ban was unclear, the decision to ban the carts came after a bomb hidden under a horse-drawn cart exploded downtown on Feb. 22, killing three civilians.

The ban on motorcycles and bicycles goes into effect at dawn Sunday, while the one on carts went into effect just after noon Saturday, said Brig. Gen. Qassim al-Moussawi, the chief Iraqi military spokesman for Baghdad.

The operation launched last February peaked in June 2007 with the deployment of thousands of extra troops to Baghdad and other parts of Iraq.

It also was bolstered by two other key elements. One was a decision by al-Sadr to declare a six-month cease-fire last August, and a plan funded by the American military to recruit and pay Sunni tribesmen and neighborhood groups to fight al-Qaida in Iraq. The groups are often referred to as "Awakening Councils."

The U.S. military has reported a 60 percent overall drop in violence around Iraq since last June.

Milano said a decision Friday by al-Sadr to extend the cease-fire six more months was "welcome news."

He added that "al-Qaida in Iraq is still our number one enemy." In the latest clashes with the group, Iraqi security forces reported killing 11 alleged al-Qaida in Iraq members during operations just north of Baghdad on Friday and Saturday.

The first operation took place Saturday near the city of Tikrit, the hometown of former Iraqi leader Saddam Hussein, and killed eight members of al-Qaida. Among those killed was a man identified as Abu Talha al-Arabi, a regional leader, the police said.

Police said two others were killed late Friday near the town of Samarra as they planted a roadside bomb, while an al-Qaida area leader was killed Saturday near Samarra, 60 miles north of Baghdad.

In an unrelated development, the U.S. military in Baghdad said its forces detained 11 suspected insurgents Friday and Saturday during operations to disrupt al-Qaida operating in the northern city of Mosul.

According to Iraqi police, a suicide bomber killed the leader of an Awakening Council in Saqlawiyah, a town in Anbar province 45 miles west of Baghdad, and his bodyguard. Fallujah police identified the leader as Sheik Ibrahim Mutayri al-Mohamaday.

Separately, the head of the Iraqi Journalists Union was shot and wounded Saturday. Shihab al-Timimi was attacked by unidentified gunmen as he was driven to an art gallery in Waziriya, near central Baghdad, police and union officials said. He had just left the nearby union headquarters.

AP Television News footage showed him with what appeared to be a gunshot wound to the chest and bandaged shoulders and arms. Al-Timimi, who is in his mid-70s, was elected president of the union in 2004. There was no immediate explanation for the attack.