Four U.S. soldiers were killed in a bomb attack in Baghdad, taking the American death toll in the Iraq War to at least 4,000, according to the independent icasualties.org group that tallies fatalities in the conflict.

The Multi-National Division - Baghdad soldiers were on patrol in the south of the capital yesterday when their vehicle was hit by a roadside bomb, the U.S. military said today in an e-mailed statement.

The deaths, days after the fifth anniversary of the U.S. invasion of Iraq, occurred on the same day Baghdad's fortified Green Zone, which houses the Iraqi government and the American embassy, was hit with mortar fire, and more than 50 people died in attacks across the country.

As the war enters its sixth year, there are growing calls from some U.S. lawmakers to accelerate a drawdown of troops after an extra 30,000 soldiers were deployed last year to halt violence between majority Shiites and minority Sunnis. Some estimates put the cost of the Iraq War at as high as $3 trillion.

President George W. Bush should change direction on the conflict and provide a clear assessment of its costs and consequences, U.S. Senator Robert Menendez said on March 22 when he delivered the Democratic party's weekly radio address.

Bush said on March 19, the fifth anniversary of the invasion, the extra forces he ordered into Iraq last year increased security in the country and paved the way for a ``major strategic victory'' in the war against terrorism.

Military Casualties

Monthly U.S. military deaths have increased from the 14 soldiers killed in December last year, the lowest since February 2004, according to Defense Department statistics.

There were 34 military deaths in January and 25 in February. As many as 26 have died in March, according to Bloomberg calculations using Defense Department statistics and press statements.

Three U.S. soldiers were killed in an attack northwest of Baghdad two days ago, the military said in a separate statement.

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