DAMASCUS, Syria (AP) -- Syria promised 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 UN 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 UN resolution that halted Israeli-Hezbollah fighting Aug. 14. The truce also calls for a beefed-up UN force of 15,000 soldiers in southern Lebanon and more nations committed troops to the mission.

The UN 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 had really 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.

She said "numerous rockets and missiles made by Syria and supplied by Syria ... were fired against Israel" by Hezbollah during the 34-day Lebanon war.

Israel wants peacekeepers to also patrol Lebanon's border with Syria, but the UN 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 UN moves onto the border.

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

The UN chief had little success in Beirut, where Prime Minister Fuad Saniora said Lebanon would be the last Arab country to make peace with the Jewish state, and in Israel, where Olmert rebuffed Annan's call for quickly lifting the blockade of Lebanon.

Assad made no comment after his talks with Annan, and Syrian news reports about the meeting did not address the issues of stopping Hezbollah weapons or relations with Lebanon.

The UN chief expressed confidence Lebanese and Syrian troops could halt the flow of Hezbollah weapons over the border without the presence of UN peacekeepers.

"I think it can happen. It may not be 100 percent, but it will make quite a lot of difference if the (Syrian) government puts in place the measures the government has discussed with me," Annan said. The Security Council resolution calls on all countries to prevent the sale or supply of weapons to entities in Lebanon without the consent of the Lebanese government or UN peacekeepers. It also calls for Lebanon to "secure its borders and other entry points."

It is not the first time Syria promised to tighten its borders. The U.S. has accused Damascus of lax security on the Syria-Iraq border, where Washington says insurgents have poured into Iraq. Syria vowed similarly to boost border patrols and work with U.S. officials, but insurgents are still believed to pass through.