Civilian and military casualties hit record highs last year as violence reached its worst levels since the Taleban were ousted in late 2001, with foreign forces launching two big offensives in the past eight months to stem a growing insurgency.

A website which tracks casualties, www.icasualties.org, said 54 US troops have been killed in Afghanistan this year, raising the total to 1,000 since the Taleban's fall. This compares with eight this year in Iraq, where 4,378 have been killed since 2003.

Afghanistan is high on US President Barack Obama's foreign policy agenda and more American casualties or a military campaign that fails to bring stability to the country in an increasingly unpopular war could harm his presidency.

The Islamist militants have made a comeback, pushing out of strongholds in the south into the east and north, and are resisting efforts by President Hamid Karzai's government to impose control.

The second of the offensives, Operation Mushtarak, was launched by NATO-led troops 10 days ago to flush militants out of the Marjah district of Helmand, where they had set up their last big stronghold in Afghanistan's most violent province.

Western forces say they have broken the Taleban's grip and only face pockets of resistance, some of it fierce, in Marjah.

But a bomb that killed at least seven civilians and wounded 14 near a government building in Helmand's capital, Lashkar Gah, underscored the vast security challenges facing NATO and Karzai's US-backed government.

"The blast was caused by explosives attached to a bicycle and was controlled remotely," said Dawud Ahmadi, spokesman for Helmand's provincial government.

He said later all the casualties were civilians and that it was unclear who set off the bomb or who was the target.

Residents said there was a busy bus station nearby.

In Zabul province, also in the south, a roadside bomb hit a convoy of Romanian soldiers serving with the NATO-led International Security Assistance Force (ISAF), said Mohammad Jan Rasoulyar, a spokesman for the provincial governor.

Five casualties were evacuated from the site, Rasoulyar said, but it was not clear if anyone had been killed.

The latest Helmand operation is an early test of Obama's plan to add 30,000 troops to win control of Taleban bastions and hand them over to Afghan authorities before the start of a gradual US troop withdrawal in 2011.

Marjah is a prime example of the challenge facing US troops and their NATO allies. They have taken over key areas but still face pockets of stiff resistance from the Taleban, who have littered roads and buildings with hidden bombs.

The success of the operation hinges on whether they can keep Taleban fighters from re-capturing their stronghold and make sure that Afghan forces can secure the area on their own.

Ultimately Marjah can only be stable once the local government provides enough jobs and economic opportunities to keep the local population on its side, eradicating conditions that breed militancy, analysts say.