Fighting between Syrian forces and rebel fighters spilled over into Turkey and Lebanon Monday, on the eve of a United Nations-brokered ceasefire that now seems to be on the brink of failure.

Syrian government forces reportedly fired across the border into a refugee camp in Turkey, killing two people and wounding three others.

According to a report from the Syrian Observatory for Human Rights, based in Britain, fighting broke out at about 4 a.m. local time when opposition fighters ambushed Syrian government troops at the Salameh border crossing.

After a protracted battle in which six Syrian soldiers were reportedly killed, eight wounded rebel fighters fled into Turkey. However, Syrian troops continued to fire on the fleeing rebels as they made their way into a refugee camp inside Turkey.

Rami Abdul-Rahman, a spokesman for the Observatory, said five people were initially injured at the camp in the town of Kilis. Two of them later died, according to rebels, but that could not be immediately confirmed.

The casualties included three Syrians, one Turkish translator and a Turkish police officer, said Gov. Yusuf Odabas in the southwestern Turkish province of Gaziantep.

The incident is believed to be the first violent incursion into Turkey, though there have been similar cross-border attacks into Lebanon, which also shares a border with Syria.

A journalist was also killed Monday in Lebanon's Wadi Khaled area as gunfire broke out in the nearby Syrian village of Armouta.

Ali Shaaban, a cameraman for the Al Jadeed television station, died from a bullet wound.

Reporter Hussein Khreis said bullets rained down on their car.

"If you see the car, you would think it was in a war zone," Khreis told Al Jadeed TV. "It is completely destroyed from the bullets."

The renewed tensions threatened a ceasefire agreement brokered by the United Nations' Kofi Annan that would see Syrian troops pull out of civilian areas by Tuesday morning. A spokesperson for the U.S. State Department said America is "absolutely outraged" by the latest attacks.

Syrian President Bashar Assad also added new demands on Sunday, saying he wanted written guarantees from rebels that they would lay down their weapons.

The country's main rebel group, the Free Syrian Army, flatly rejected that demand.

"We as protectors of the Syrian people announce a cease-fire against the regime's army starting on the morning of April 10 and we will stick to this promise if the regime abides by the clauses of the initiative," a member of the FSA's military council said in a video posted to YouTube.

Assad also said he wants other Arab countries and diaspora groups to stop funding the rebels and providing them with firearms.

Bessma Momani, a senior fellow with the Waterloo, Ont.-based Centre for International Governance Innovation, said it seems that Assad's agreement to the ceasefire was merely a stalling tactic.

"We saw more troop deployment to different areas, we saw the first use of helicopters. What we've seen is actually an intensification of the offensive rather than withdrawal of troops," she told CTV's Power Play on Monday.

"Clearly this was 10 days of delay that Assad used to try to intensify his operations and, unfortunately, I think we all fell for it."

Momani said it's also troubling to see Assad making last-minute demands before the ceasefire is set to begin.

Security analyst Kamran Bokhari, director of Middle Eastern and South Asian affairs with STRATFOR, said should tensions continue to escalate between Turkey and Syria, it will raise new questions for the international community about what action it could or should take in the region.

"The international community will then have to look at a new dynamic in which the Turks are having to deal with cross-border firing, not just the influx of refugees that is already adding a lot of strain on Ankara," Bokhari told CTV News Channel.

Meanwhile, the international community's unwillingness to interfere militarily has been interpreted by Assad as "a green light to continue his atrocities," Momani said.

She said Syria's only supporters – Russia and China – will now have to figure out a new approach to the situation since they will be "embarrassed before the international community" for touting Assad's supposed commitment to ending the bloodshed.

"What happens between those two allies, how they react in the coming days I think will really, hopefully change the dynamics here," Momani said.

Death toll estimated at 9,000

There are an estimated 24,000 Syrian refugees currently living in Turkey. An estimated 9,000 people have been killed in Syria since the fighting began last summer when protests first began against Assad's regime.

Protests that initially began as peaceful have become increasingly violent in recent months as the government wages a brutal crackdown.

There are reports that more than 100 people, mostly civilians, have been executed by Syrian forces. The New York-based group Human Rights Watch said it has documented the executions of 85 civilians, including women and children, and at least 16 wounded or captured rebel fighters.

That estimate is likely at the low end of the spectrum, the group said, because it only included cases that could be corroborated by witnesses.

"In a desperate attempt to crush the uprising, Syrian forces have executed people in cold blood, civilians and opposition fighters alike," said Ole Solvang, a researcher for the group.

"They are doing it in broad daylight and in front of witnesses, evidently not concerned about any accountability for their crimes."

With files from The Associated Press