Assailants ambushed a convoy of security contractors traveling to Baghdad's airport, killing two Americans and two Poles working for a U.S. security company in Iraq, their employer said Sunday.

Gunmen opened fire with automatic weapons as the security guards working for Blackwater USA (search) traveled to the airport to pick up a client, a company official in Baghdad said while speaking on condition of anonymity.

Four men died on the spot, but three others managed to fight their way to the other side of the road, flag down a passing car, and travel to safety with U.S. coalition forces at their headquarters in the Green Zone (search) in central Baghdad.

A spokesman for Moyock, N.C.-based Blackwater, Chris Bertelli, said the convoy was "attacked from a couple of different angles by four or five vehicles with four or five people each."

"They at least had automatic weapons if not RPGs," or rocket-propelled grenades, Bertelli said.

Bertelli declined to identify the two Poles and two Americans killed in the attack. He said they and three other Blackwater guards who survived the attack were working for a delivery subcontractor for Texas-based KBR, a division of Halliburton Co (search). The subcontractor, called ESS, generally transports food and kitchen equipment within Iraq.

Though the major road is heavily traveled, it "seems to be one where ambushes are not unheard of in that area," Bertelli said.

In Warsaw, Boguslaw Majewski, the spokesman for Poland's Foreign Ministry, also reported the deaths.

Majewski said an "intense search" for the attackers was under way. He said another Pole was also slightly injured in the attack, but gave no other details.

Blackwater is one of the biggest and best-known private security firms working in Iraq.

Four other civilian security personnel from Blackwater were killed March 31 after their vehicle was hit by rocket-propelled grenades in Fallujah. Their bodies were mutilated and burned, and two were hung from the framework of a bridge across the Euphrates river.

Nearly a week after that killing, U.S. Marines laid siege to Fallujah (search), one of the main centers of the anti-American insurgency in Sunni Arab-dominated areas of Iraq. The fighting lasted for three weeks until the Marines handed over control of the city to a freshly-created all-Iraqi force that promised to find and arrest the attackers.

No arrests have been made so far.

Bertelli also said that Blackwater has also lost another contract worker in Iraq who died in a traffic accident. The company has about 450 security guards working under contract in Iraq, he said.

"Of course our prayers are with those who survived as well as those who were killed," he said.

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Associated Press Writer Emery P. Dalesio in Raleigh, N.C., contributed to this story.