KABUL (Reuters) – A U.S. soldier and a U.S. Marine have been killed in militant attacks in Afghanistan, bringing American combat deaths in the country this year to 51, the bloodiest period for U.S. forces since the fall of the Taliban.

The casualties in Kandahar and Kunar provinces on Monday took U.S. deaths in Afghanistan in two days to seven. A Chinook military transport helicopter crashed on an anti-militant mission in Zabul province on Sunday, killing its crew of five.

A military statement on Tuesday said the soldier was killed after his unit came under rocket-grenade and small-arms fire west of the city of Kandahar, while the Marine died in a similar attack on a forward base near the eastern town of Asadabad.

An American soldier was in stable condition after being wounded in the first attack, in which two militants were killed and another wounded, the statement said. U.S. forces responded to the latter attack with mortars and aircraft, it said.

&#34These men gave their lives for America and a free Afghanistan,&#34 Brigadier-General James G. Champion, deputy commander for U.S. operations in Afghanistan, said in the statement. &#34We will continue to aggressively take the fight to the enemy until they are defeated.&#34

The United States overthrew the Taliban in late 2001 for refusing to give up al Qaeda leader Osama bin Laden, mastermind of the September 11 attacks on U.S. cities. It leads a multinational force of about 20,000 troops pursuing militants in the country.

This year saw a surge in violence in the run-up to legislative elections held on September 18, in which more than 1,000 people, most of them insurgents, died.

The latest casualties came despite post-election comments from Afghan President Hamid Karzai calling for a change in strategy in the war against insurgents.

Karzai said he did not think there was a big need for military action any more, and questioned the use of U.S. air strikes, some of which have caused civilian casualties.

U.S. defense officials have said that, while they agree with Karzai on air strikes, they still see the need for military action. The Taliban vowed last week to step up its insurgency after failing to derail the election.

U.S. President George W. Bush”s national security adviser, Stephen Hadley, said in Kabul on Monday there was no quick fix for the problem of Islamist militancy and much closer cooperation was needed between Afghanistan, neighbouring Pakistan and Washington.