BEIRUT -- A TV journalist in Lebanon and at least two people in a refugee camp in Turkey were killed Monday when Syrian forces fired across two tense borders.
A planned cease-fire seems all but certain to fail.
Activists reported heavy violence across Syria with more than 125 killed in the past two days.
The Obama Administration expressed outrage at the violence spilling over Syria's frontiers. It said the Syrian government appeared to have little commitment to the peace plan negotiated by former U.N. chief Kofi Annan.
The latest bloodshed was a sign of how easily Syria's neighbors could be drawn into a regional conflagration. Syrian President Bashar Assad's crackdown on a year-old uprising has become increasingly militarized, despite diplomatic efforts.
Mr. Annan brokered a deal that was supposed to begin with Syria pulling its troops out of population centers by Tuesday morning. A full cease-fire by both sides was to follow within 48 hours.
Hopes for that plan collapsed after the fresh wave of violence and new demands by the Syrian government for written guarantees that the opposition would lay down its weapons first.
Naci Koru, Turkey's deputy foreign minister, said Tuesday's deadline for the withdrawal has become "void at this stage," state-run TRT television reported.
On Monday, Syrian forces fired across the border into a refugee camp in Turkey, wounding at least six people, Turkish authorities said.
Four witnesses in the camp told the Associated Press that two people in the camp also had been shot and killed.
The soldiers were believed to be firing at rebels who tried to escape to the refugee camp after ambushing a Syrian military checkpoint and killing six soldiers, according to the Britain-based activist group Syrian Observatory for Human Rights.
The troops kept firing as they pursued the rebels, who made a run for the camp, sending bullets whizzing across the frontier, the Observatory said.
Turkish authorities said four Syrians and two Turks were wounded, including a Turkish translator who had entered the camp to try to calm an anti-Assad protest.
The Turkish Foreign Ministry also reported two deaths, but under different circumstances than the witnesses described.
According to the ministry, 21 wounded Syrians were brought to Turkey Monday, but two of them died soon afterward. It was not possible to reconcile the two accounts.
Turkey shelters 24,000 Syrian refugees, including hundreds of army defectors, and has floated the idea of setting up a buffer zone in Syria if the flow of displaced people across its border becomes overwhelming.
The countries share a 566-mile border. Parts of southern Turkey are informal logistics bases for rebels, who collect food and other supplies and smuggle them to comrades across the border in Syria.
Monday's shooting was believed to be the first within Turkey, although there have been similar cross-border attacks into Lebanon.
Syrian troops fired about 40 rounds across the border into northern Lebanon, killing a cameraman for the Lebanese television station Al Jadeed, the station said. The camera crew was reportedly in Lebanese territory.
Ali Shaaban, born in 1980, was shot in the chest as he sat in a car, and he died on the way to the hospital, Lebanese security officials said.
U.S. Statement Department spokesman Victoria Nuland said Monday: "These incidents are just another indication that the Assad regime does not seem at all willing to meet the commitments that it made to Kofi Annan. Not only has the violence not abated, it has been worse in recent days."
Ms. Nuland said the Syrian government was trying to "stall for time" with its demand for a written guarantee that opposition forces would disarm before it withdraws troops from cities and towns.
"This is just more chaff being thrown up in the air at the last minute to deflect attention from the fact that the regime is not meeting the commitments," she said.
The U.N. estimates 9,000 people have been killed in Syria since March, 2011, when the uprising began with mostly peaceful protests against Mr. Assad. After a government crackdown many Syrians took up arms.