BAGHDAD, Iraq (CNN) -- Seven U.S. troops were killed in Iraq on Thursday, the U.S. military said on Friday.
U.S. soldiers return to base Thursday after going after al Qaeda in Iraq militants outside Baghdad.
Four Marines assigned to Multi National Force-West were killed during a combat operation in Anbar province, the Sunni-dominated territory west of Baghdad.
Three U.S. soldiers assigned to Task Force Lightning were killed by an explosion near their vehicle in Nineveh province in northern Iraq.
The number of U.S. military deaths is the Iraq war stands at 3,760. The number in September alone is 18.
Meanwhile, Britain's Defense Ministry said Friday that a British soldier was killed in Iraq Wednesday while "conducting routine operations." The death brings to 169 the number of British military personnel killed in Iraq.
On Friday, the top U.S. general in Iraq, Gen. David Petraeus, released a letter to U.S. troops saying military progress in the conflict has been "uneven" but that coalition forces have "tactical momentum."
"We are, in short, a long way from the goal line, but we do have the ball and we are driving down the field," said Petraeus, who will next week report to Congress on progress in Iraq.
About 26,000 U.S. and Iraqi forces are taking part in an offensive against al Qaeda in Iraq in northern Iraq, the U.S. military said on Thursday.
The operation, Lightning Hammer II, is an extension of an earlier operation in Diyala province.
About 14,000 Iraqi security forces stationed throughout Nineveh province and 12,000 U.S. soldiers are conducting the operation, which started Wednesday evening.
The military said the operation "follows Lightning Hammer I ... to deny al Qaeda safe haven in the provinces" of Salaheddin, Nineveh, Diyala, and Kirkuk.
The military said the original Operation Lightning Hammer -- August 13 to September 1 -- ousted militants from the Diyala River valley, northeast of Baquba, the capital of Diyala province. E-mail to a friend