On more than 30 occasions so far this year, members of the Afghan security forces have opened fire on their Western allies, killing at least 45 foreign troops, the majority of them American.

Afghan defense ministry spokesman General Zahir Azimi said at a news conference on Wednesday that the attacks were "a matter of concern" for the Afghan government.

"So far, hundreds of people have either been arrested or expelled from the army. We have found evidence against some people and some suspicious people have been arrested," he said.

When asked by reporters for further details, Azimi gave no breakdown on precise numbers.

"All the soldiers who have been either arrested or expelled are Afghans, there are not foreigners among them," he said.

The arrests and expulsions came as NATO's head called Afghan President Hamid Karzai Wednesday to express "deep concerns" about a surge in rogue attacks.

In a telephone call with Karzai, NATO Secretary-General Anders Fogh Rasmussen "reaffirmed our continued commitment to the International Security Assistance Force mission and emphasized that the strategy remains on track," NATO spokeswoman Carmen Romero said.

"The secretary-general, however, also shared with President Karzai his deep concerns about insider attacks," she said.

AFP - Reuters