By Paul Tait

KABUL (Reuters) - Four U.S. soldiers were killed by roadside bombs in southern Afghanistan on Saturday, the U.S. military said on Sunday, the latest casualties in an escalation of insurgent violence.

A fifth soldier serving with NATO-led forces in the south died on Friday from wounds received in June, the alliance said in a statement.

Thousands of U.S. Marines and hundreds of British troops have been fighting major new offensives in the past 10 days in Helmand province, a Taliban stronghold and Afghanistan's biggest producer of the opium that funds the insurgency.

"The four killed in two IED attacks were U.S. service members," said U.S. military spokeswoman Lieutenant Commander Christine Sidenstricker, referring to improvised explosive devices, or roadside bombs, one of the most common weapons used by insurgents to attack Afghan and foreign security forces.