JAN OLSEN in COPENHAGEN and IAN BRUCE Denmark's military intelligence agency is investigating whether Iraqi insurgents have used mobile phone records to track down and threaten relatives of Danish soldiers in Iraq.

Family members of several soldiers have claimed they had threatening phone calls from unidentified callers in Iraq.

The callers may have tracked down the numbers by monitoring the soldiers' private phone calls, according to the Danish Defence Intelligence Service (DDIS).

"We're mapping the extent of the threats after which we will consider whether our guidelines to our staff and their families regarding the use of mobile phones and e-mails should be revised," said agency spokeswoman Mette Noehr.

She said the DDIS was not sure whether insurgents were behind the calls.

"It could also be hoodlums but one thing is sure, we're taking this very seriously," she said.

Denmark withdrew its 460-strong contingent from the southern city of Basra last month and replaced it with a small helicopter unit. Seven Danes have been killed in Iraq.

Private Ralf Clemmesen, who served in Iraq in the first half of 2007, said his father and girlfriend had received threatening phone calls from Iraq in February.

"I couldn't do anything. I was locked in Iraq. It didn't improve my concentration," he said, adding the relatives of at least 10 Danish soldiers had received similar calls.

In another sign of the stresses on serving soldiers, it has emerged the US army's suicide rate last year was the highest since 1981. More than one in four of those who took their own lives did so while serving in Iraq or Afghanistan.

A Pentagon report shows 99 soldiers committed suicide in 2006, compared with 88 the previous year. Most shot themselves with their own weapons.

The 2006 toll included 28 on duty in the two war zones.

The report confirms that extended tours of up to 15 months in Iraq produced most suicides and was the most common location for successful and unsuccessful attempts by soldiers to take their lives.

Pentagon sources say US troops will have to endure extended tours of duty until at least next summer because of overstretch and the demands of fighting two wars simultaneously.

In Iraq yesterday, angry members of the minority Yazidi sect said they feared annihilation after scores of villagers were killed in possibly the worst suicide bomb attack of the four-year conflict.

Estimates of the death toll from Tuesday's attack varied from 175 to 500.

"Their aim is to annihilate us, to create trouble and kill all the Yazidis because we are not Muslims," said Abu Saeed, an old man in the village of Kahtaniya.

He told Deputy Prime Minister Barham Salih that 51 members of his extended family had been killed.

The US military has said al Qaeda is the prime suspect for the bombings.

It had said large-scale attacks were possible before a progress report on the conflict is delivered to Congress on September 15.