Iraq has denounced a raid into Syria at the weekend, saying it does not want its territory to be used as a launch-point for US attacks on its neighbours.
Syria has also condemned the attack, which it said killed eight civilians, as an act of “terrorist aggression”.
Unnamed US officials have said the operation killed a key figure involved in the smuggling of fighters into Iraq.
Meanwhile, Iraq’s cabinet authorised PM Nouri Maliki to put forward proposed changes to a security pact with the US.
A government spokesman said the suggested amendments, agreed at a cabinet meeting, addressed both the wording and the content of the Status of Forces Agreement.
The deal, known as SOFA, will govern US troop presence in Iraq when a UN mandate expires at the end of 2008.
The US and Iraqi governments had previously said the pact, which would authorise the presence of US troops in Iraq until 2011, was final and could not be amended – only accepted or rejected by the Iraqi parliament.
Speaking after the cabinet meeting, government spokesman Ali al-Dabbagh explicitly criticised the US over the reported helicopter strike.
“The Iraqi government rejects the US helicopter strike on Syrian territory, considering that Iraq’s constitution does not allow its land to be a base for launching attacks on neighbouring countries,” he said.
“We call upon American forces not to repeat such activities and Baghdad has launched an investigation into the strike.”
But he urged Damascus to prevent groups using Syrian territory for “training and sending terrorists for attacks on Iraq and its people”.
The White House has neither confirmed nor denied Sunday’s strike near Abu Kamal, some eight kilometres (five miles) north of Iraq’s border with Syria.
An unnamed US official told Reuters news agency the raid killed Iraqi Abu Ghadiyah, a former lieutenant of Abu Musab al-Zarqawi, the al-Qaeda in Iraq leader who was killed in 2006.
“It was a successful operation. [Abu Ghadiyah] is believed to be dead. This undoubtedly will have a debilitating effect on this foreign fighter smuggling network,” the official said.
A second official told the agency that only people the forces considered a threat had been targeted and that women and children were alive when the team left.
A US intelligence official told Associated Press news agency there was information that Abu Ghadiyah was about to carry out an attack in Iraq and that this had led to the raid.
If confirmed, Sunday’s strike would be the first US attack in Syria since the US-led invasion of Iraq in 2003.
The attack took place during the afternoon rest period, with a troop assault preferred over a missile strike to reduce civilian casualties, the intelligence official said.
It’s hard to believe the Syrians could not see this coming
The US had repeatedly asked Syria to hand over Abu Ghadiyah but Damascus said it was monitoring his activities, another US military official told AP.
Newly released amateur footage said to show the raid shows villagers pointing to the sky as helicopters fly in.
The mobile phone video does not show any landings but has images purportedly from after the attack, showing a crowd looking at blood-stained bodies. The authenticity of the video has not been verified.
Syria’s Foreign Minister Walid Muallem said all the victims – a father and his three children, a farm guard and his wife, and a fisherman – were civilian.
He said: “Killing civilians in international law means a terrorist aggression. We consider this criminal and terrorist action.”
Mr Muallem, speaking in London, said the US knew “full well that we stand against al-Qaeda. They know full well we are trying to tighten our border with Iraq”.
Asked if Syria would use force if a similar operation was mounted, he said: “As long as you are saying if, I tell you, if they do it again, we will defend our territories.”