Damascus, Syria ? Syria promised Friday to increase border patrols and work with Lebanese troops to thwart the flow of arms to its ally Hezbollah, but Israel questioned whether the Damascus regime would be a “reliable force” in guarding the border.

If carried out, the promises made by Syrian President Bashar Assad to U.N. Secretary-General Kofi Annan would be a major boost to efforts to keep the peace in Lebanon.

Preventing weapons from reaching Hezbollah is a key element of the U.N. resolution that halted Israeli-Hezbollah fighting Aug. 14. The truce also calls for a beefed-up U.N. force of 15,000 soldiers in southern Lebanon. More nations committed troops to the mission Friday, and Indonesia said today it would send up to 1,000 troops by the month’s end after Israel dropped objections to its participation in the U.N. peacekeeping force.

The U.N. chief said that if Syria follows through in tightening control of the border, peace efforts will be greatly helped. “I have no reason to believe it will not be done,” Annan said.

But Israel pointed to Syria’s past role in allegedly supplying weapons to the Shiite guerrillas of Hezbollah and said it doubted Assad’s regime really had changed its stance.

“Israel does not think that Syria : has shown any reason to be a reliable force,” said Miri Eisin, a spokeswoman for Israeli Prime Minister Ehud Olmert.

Israel wants peacekeepers to also patrol Lebanon’s border with Syria, but the U.N. truce does not give them the mandate to do so without permission from the Lebanese government. Israel has said it will not lift its punishing air and sea blockade of Lebanon until the U.N. moves onto the border.

Syria has said the deployment of U.N. troops along the border would be a “hostile” affront, and Annan said Assad repeated his opposition to it during their meeting.

While it remains to be borne out, Syria’s vow to help implement the U.N. resolution was Annan’s biggest diplomatic feat during an 11-day Mideast tour.

Annan flies today to Iran, Hezbollah’s other main backer.