Syrian troops stormed a central town and a northwestern region in search of regime opponents on Saturday, activists said, a day after the government agreed in principle to allow the Arab League to send observers to oversee a peace plan proposed by the 22-member bloc.

The attacks on the town of Shezar in the central province of Hama and on the restive Jabal al-Zawiya region near the Turkish border came as pressure mounted on Damascus to end its eight-month crackdown on anti-government protesters. The unrest has killed more than 3,500 people since mid-March, according to U.N. estimates.

The British-based Syrian Observatory for Human Rights and another activist group called the Local Coordination Committees said land and cellular telephone lines as well as electricity were cut in the Jabal al-Zawiya region, where army defectors have been active for months.

Elsewhere, two army defectors were killed in a clash with troops in Qusair near the border with Lebanon, while a civilian was killed by security forces in Hama, said the observatory. The Local Coordination Committees had a different toll, saying one person was killed in Qusair and one in the central city of Homs.

Syria agreed in principle Friday to allow dozens of Arab observers into the country to oversee an Arab League peace plan that calls on the government to stop attacking demonstrators, pull tanks out of cities and begin negotiations with the opposition.

It was a significant concession from a hard-line regime that loathes any sort of outside interference. But critics say the government is only stalling, trying to defuse international pressure while continuing its bloody crackdown.

The Arab League has already suspended Syria's membership in the bloc for failing to abide by the peace plan. On Wednesday, the league gave Damascus three days to accept the observer mission or face economic sanctions.

Violence has escalated in Syria over the past week, as army dissidents who sided with the protests have grown more bold, fighting back against regime forces and even assaulting military bases. Activist groups said security forces on Friday killed at least 16 anti-government protesters.

Pressure from European capitals and the U.S. is also building on President Bashar Assad to end the bloodshed.

An official at Britain's Foreign Office said Foreign Secretary William Hague intends to meet opposition representatives in London on Monday.

French Foreign Minister Alain Juppe called on the U.N. Security Council to strengthen sanctions against Assad's regime. However, Russia, which holds veto power in the council, urged caution in moving against Damascus.

In Washington, State Department spokesman Mark Toner said the U.S. has seen no signs that Syria's government will honor the Arab League proposal.

Syria's neighbor to the north, Turkey, has become one its most vocal critics, a notable shift because the two countries once had close political and economic ties.

On Saturday, Turkish Prime Minister Recep Tayyip Erdogan, commenting on the deteriorating relations between his country and its southern neighbor, accused Syria of not fulfilling promises for reform or to stop the bloodshed.

"In the past nine years, it was Syria and the Syrian people _ rather than Turkey _ that had benefited from the Turkish-Syrian friendship," Erdogan said.

"... Syria has not kept its promises to Turkey, to the Arab League or to the world. It made promises but did not fulfill them. It has not acted in a sincere trustworthy manner," he said.

The attacks on Jabal al-Zawiya came two days after an army force in the nearby area of Wadi al-Deif came under attack by army defectors, a clash that lasted four hours and left an unknown number of casualties among troops loyal to Assad, an activist said.

The activist, who spoke on condition of anonymity because of the sensitivity of the matter, said troops fired heavy machine guns mounted on armored personnel carriers.

The Arab League observer mission aims to prevent violence and monitor a cease-fire that Damascus agreed to last week but has been unwilling _ or unable _ to implement.

Nabil Elaraby, the head of the Arab League, said in a statement Friday that he received "amendments" to the monitoring mission from Damascus, which the league is studying. He gave no details on the changes Syria seeks.

The original league proposal had been for a 500-member observer mission but the number has dropped to 40, said Ibrahim el-Zaafarani, an Egyptian member of the Arab Medical Union who is expected to be part of the team for Syria. He said it was not clear why or on whose behest the number was reduced.

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Associated Press writers Suzan Fraser in Ankara, Turkey, and Meera Selva in London contributed to this report.

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Bassem Mroue can be reached on http://twitter.com/bmroue