KABUL: Roadside bombs killed four US soldiers in southern Afghanistan, the US military said Sunday, the latest deaths in an escalation of violence that has put pressure on coalition leaders over their war strategy.

Thousands of US Marines and hundreds of British soldiers have been fighting a major new offensive in the past 10 days in Helmand province, a Taleban stronghold and Afghanistan’s biggest producer of the opium that funds the insurgency.

The Taleban backlash has put pressure on leaders in Washington and London, who say US and other NATO-led troops have pushed back Taleban insurgents but that a lot of tough fighting remains to be done during the summer.

US President Barack Obama told Sky News on Saturday that the United States and its allies would have to evaluate Afghanistan again after next month’s presidential election.