"I wouldn't say there's a breakdown in security. I would say that there is a ... persistent and consistent pattern of attacks but it fluctuates. There are spikes and there are less active periods," deputy State Department spokesman Adam Ereli told reporters.

He was asked whether attacks by insurgents of late depicted a possible breakdown in security in Iraq, where there was still no new government since the Shiites swept the January 30 elections.

Ereli said the United States and the multinational force in Iraq as well as the local authorities recognized the insurgent attacks "as something that requires our full attention and our unwavering efforts to combat."

Insurgents killed at least 10 foreign security specialists working in Iraq in three separate attacks over two days, including six Americans who died when their helicopter was shot down by a missile Thursday.

The six US citizens were among 11 killed when the Bulgarian commercial helicopter was brought down north of Baghdad.

Thursday's attack came after the killing of an American, an Australian and a Canadian security specialist in an ambush on their convoy on Wednesday, said their employer, the British-based Edinburgh Risk security firm.

Thousands of security specialists, mostly former soldiers, currently work in Iraq, helping to protect coalition facilities along with employees of private organisations and foreign news teams.

Also this week, 60 corpses were reportedly found in an Iraqi river, which President Jalal Talabani said were of Shiite hostages seized in a kidnap drama so far shrouded in mystery.

Iraqi police also said Wednesday that 19 Iraqi soldiers were found executed in a stadium.

Despite the violence, Ereli said there were "a couple of positive trends" -- more Iraqis were being trained to provide security and that they were taking "very effective actions" to confront the insurgency.

They certainly are part of a broader strategy to have a "free, prosperous and stable Iraq," he said.

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