American officials say insurgent violence in Afghanistan has risen to its highest level since the Taliban were toppled in 2001.
Insurgent attacks soared 59% to 5,222 incidents from January to May, compared with 3,283 attacks in the first five months of 2008.
US-led forces toppled Afghanistan's former Taliban regime in 2001 after the 11 September 2001 attacks on New York and Washington, which US officials say were planned from al-Qaeda safe havens on Afghan territory.
"There are some tough months ahead. Some of this violence will go up because we are going to go after their sanctuaries and their safe havens as we must," Army General David Petraeus said.
The United States has already increased its military presence in Afghanistan to 56,000 troops, from about 32,000 in late 2008.
General Petraeus said he expects to see a total 68,000 troops in the war zone by autumn.