KABUL: Four NATO soldiers, two of them part of the anti-Taliban offensive known as Operation Mushtarak, were killed in Afghanistan over the weekend, the alliance said Sunday.

The NATO-run International Security Assistance Force said two soldiers were killed on Saturday, one by a bomb in the course of the Mushtarak operation in the Marjah area, the other in the east of the country by an indirect hit from an unspecified projectile.

On Sunday two more soldiers were killed, one by "indirect fire" in the course of Mushtarak, the other by a bomb elsewhere in the south of the country, NATO said.

It did not reveal the soldiers' nationalities, in line with NATO policy.

Some 15,000 US, NATO and Afghan troops are involved in the Mushtarak operation in Helmand province, which is aimed at clearing the Taliban from Marjah and its surrounds.

In total, 14 NATO soldiers have been killed in Operation Mushtarak, which began on February 13.

The latest deaths mean 93 foreign soldiers have died in Afghanistan overall since the start of the year, according to the website icasualties.org, which tracks such killings.

Taliban fighters are said by military officials to be putting up "determined" resistance in pockets of the area targeted by Mushtarak.

In addition, innumerable hidden bombs have been planted, hampering the progress of the mission.

Senior commanders have said they expect the assault to last up to a month.