Activists report Syria's shaky cease-fire has started to falter, less than a day after taking effect.

The British-based Syrian Observatory for Human Rights says Syrian troops clashed with rebel forces in the northwestern village of Khirbel el-Joz, near the Turkish border Friday. The group said the army deployed tanks to the area before the fighting broke out.

Reports of renewed fighting come as Syria's opposition forces are calling for widespread protests later in the day to test the Syrian government's resolve to abide by the truce.

The United Nations-brokered cease-fire went into effect at 6 a.m. local time on Thursday, though rights activists accused the Syrian regime of killing at least three civilians after the cease-fire deadline passed.

Later Thursday, U.N.-Arab League envoy Kofi Annan warned the U.N. Security Council that Syria had not fully complied with the terms of the peace plan. Still, Annan said he had been encouraged by reports the cease-fire was holding.

Western nations had been pushing the Security Council to send two waves of observers to Syria to monitor and enforce the cease-fire. A draft resolution calls for Syria to give the observers full and unimpeded freedom of movement across the country. It also demands Syria withdraw troops and heavy weapons from population centers.

Moscow, at times at odds with other members of the security council over the wording of resolutions aimed at Syria, has called for all parties to show “maximum prudence.”

Syrian envoy Bashar Ja'afari Thursday defended President Bashar al-Assad's regime, saying the government had ended attacks and expects opposition militias to do the same. Ja'afari blamed anti-government forces for several violent acts that he said occurred after the cease-fire deadline and said “the moment of truth has come.”

U.S. President Barack Obama and French President Nicolas Sarkozy issued a joint statement urging Syria to abide by Annan's plan.

U.S. Secretary of State Hillary Clinton also said Syrian President Bashar al-Assad cannot “pick and choose” which parts of the agreements he wants to accept. She said Washington supports sending a U.N. monitoring mission to Syria.

U.N. chief Ban Ki-moon said the international community must be united if it is going to keep Syria from descending into “chaos.” Mr. Ban said plans were under way to send observers to Syria. Diplomats said the first U.N. monitors could be dispatched as early as Friday.