KABUL (Reuters) - A U.S. service member was killed as the deadliest month for foreign troops in the Afghanistan war drew to a close, the U.S. military said on Friday, with commanders vowing to continue the fight despite the toll.

The death in southern Afghanistan brought to 40 the number of U.S. troops killed in July, by far the heaviest monthly toll in the 8-year-old war. The worst previous month for U.S. forces was in September 2008, when 26 were killed.

The latest death occurred in a firefight with insurgents in southern Afghanistan on Thursday, the U.S. military said, without giving further details. At least 70 foreign troops have been killed in July.

Britain has suffered its worst battlefield casualties since the 1980s Falklands War, with the 22 troops killed in the month taking its total losses in Afghanistan to 191, 12 more than were killed in the Iraq war.

Casualties spiked after thousands of U.S. and British troops this month launched major operations in southern Helmand province, a Taliban stronghold and the center of Afghanistan’s opium production.

“We understood the return of security to these areas would not be achieved without sacrifice,” said U.S. Rear Admiral Greg Smith, chief spokesman for U.S. and NATO forces in Afghanistan.

“For some that has come at a high price,” he told Reuters.

“CLEAR, HOLD, BUILD”

The Helmand operations are the first under U.S. President Barack Obama’s new regional strategy to defeat the Taliban and its Islamist militant allies and stabilize Afghanistan. They come before crucial presidential elections on August 20.

They are also the first phase of a new “clear, hold and build” strategy introduced after criticism that previous strategies lacked cohesion and direction.

The operations are designed to clear areas of insurgents and then hold them, something that overstretched British-led NATO forces had been unable to do before this month.

“It’s too early to assess the true impact of operations in the south. The clearing of insurgents continues and will for many more weeks to come,” Smith said.

The United States has around 62,000 troops in Afghanistan, out of a total foreign force of about 101,000. U.S. forces are set to rise to some 68,000 by the end of the year.

A mortar team attached to the U.S. Army's Dagger Company, 2-12 Infantry, 4th Brigade fires a 120mm mortar as they take fire on Michigan Base in the Pesh Valley in Afghanistan's Kunar Province July 19, 2009. REUTERS/Tim Wimborne

The extra troops include 4,000 meant to help train Afghan security forces and will be followed by a “civilian surge” of several hundred meant to help Afghanistan rebuild institutions shattered by decades of war.

General Stanley McChrystal, the new commander of U.S. and NATO forces in Afghanistan, has also introduced a new counter-insurgency strategy and issued a new tactical directive, which includes limiting the use of air strikes, aimed at reducing the number of civilian casualties in the war.

Civilian deaths have outraged many Afghans and caused friction between Washington and Afghan President Hamid Karzai’s government.

A U.N. report released in Geneva on Friday found that 1,013 civilians had been killed between January and June this year, up from 818 in the same period last year, as the battlefield in Afghanistan increasingly moved into residential areas.

The deaths were largely caused by air strikes, car bombs and suicide attacks, with the Taliban blamed for 59 percent of the fatalities, the United Nations mission in Afghanistan said.

“All parties involved in this conflict should take all measures to protect civilians, and to ensure the independent investigation of all civilian casualties, as well as justice and remedies for the victims,” said U.N. High Commissioner for Human Rights Navi Pillay.

Six civilians were killed or wounded by a roadside bomb in Jawzjan province in Afghanistan’s north late on Thursday, the Interior Ministry said.

In southeastern Ghazni province, Afghan and NATO troops killed 11 Taliban insurgents on Thursday, local officials said.