Violence across Syria killed at least 22 people — most of them civilians — as Arab leaders in Baghdad backed a peace plan during a summit focused on resolving the year-long Syrian crisis.

Syrian rights activists say forces loyal to President Bashar al-Assad killed at least 16 civilians in assaults on opposition hubs in central Syria and the northern province of Idlib on Thursday. The activists say rebels killed two soldiers in an ambush in Hama province. In other violence, Syrian state news agency SANA says “terrorists” shot and killed two army colonels in the city of Aleppo.

Arab leaders and envoys discussed a response to the Syrian crisis at a Baghdad summit — the first to be held by the Arab League in the Iraqi capital since Iraq's 1990 invasion of Kuwait. A rocket exploded near the fortified Green Zone where the summit was being held but caused no casualties.

Arab League members called on the Syrian government and opposition to implement the terms of a peace plan drafted by international envoy Kofi Annan. The plan urges both sides to start a cease-fire and a dialogue but does not call for Mr. Assad to step down as part of a political transition.

Arab leaders previously had urged the Syrian president to hand power to a deputy to manage the transition, but now they appear to have backed away from that demand.

Mr. Assad said he will “spare no effort” to ensure the success of the Annan peace plan. In remarks published by SANA on Thursday, the Syrian president promised to start a national dialogue “in a very short period.” But he also said countries providing money and weapons to the Syrian opposition must stop immediately to enable Mr. Annan's mission to succeed.

U.N. Secretary-General Ban Ki-moon said it is “essential” for the Syrian president to put his commitments into immediate effect. Speaking to Arab leaders at the start of the Baghdad summit, Mr. Ban also accused the Syrian government of failing to fulfill its responsibility to protect its own people.

Only nine leaders of the Arab League's 22 members traveled to Iraq for the summit. Mr. Assad was not invited. The absence of other leaders reflected ongoing divisions within the Arab League about how to end Syria's violence.

Qatar and Saudi Arabia were among the nations that sent low-level envoys to the summit. Both have called for tougher action on Syria, including the arming of rebels trying to end Mr. Assad's 11-year autocratic rule. Iraq, the summit host, has criticized such proposals, fearing they would further destabilize Syria, a neighbor and trading partner.

Iraqi President Jalal Talabani urged summit participants to respond to political upheavals in the Arab world by creating a “suitable atmosphere for dialogue so as to avoid violence, chaos and foreign intervention.”

Kuwait's emir was one of the nine visiting leaders. It is the first time a Kuwaiti head of state has traveled to Iraq since the 1990 invasion by the forces of former Iraqi leader Saddam Hussein.

Iraqi authorities sharply increased security for the summit, hoping to show neighboring states that Iraq can maintain stability following the withdrawal of U.S. forces last December.

Meanwhile, Britain announced that it will provide $800,000 million in non-lethal support to anti-Assad activists inside Syria to help them document government rights violations and develop skills to build a democratic post-Assad society.

The United Nations says violence linked to Syria's crackdown on the revolt has killed more than 9,000 people.