Chopper downed by hostile fire; 4 Americans killed

Four Americans and a Briton were killed in southern Afghanistan on Wednesday, military officials said.

The four U.S. service members were killed when their helicopter was downed by hostile fire in Helmand province, said International Security Assistance Force spokesman Lt. Col. Joseph T. Breasseale. 

The British soldier was killed in an explosion, also in Helmand province, the British Ministry of Defence said.

June is turning into a deadly month for international forces in Afghanistan - 29 service members, including 19 Americans, have been killed, bringing the American death toll in Afghanistan to more than 1,000, according to CNN's calculations.

"It's been a tough week," said Pentagon spokesman Bryan Whitman. "Our operational tempo is at an all-time high. We try to do everything to prevent casualties, but we have active operations and more forces there than ever in the past."

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