The commander of U.S. forces in South Asia and the Middle East said violence in Afghanistan last week reached the highest level since the 2001 U.S.-led invasion.
General David Petraeus made the comment during a speech before an audience at the Center for a New American Security in Washington Thursday.
In Afghanistan, NATO said its troops and Afghan forces have killed a "significant number" of insurgents in a major battle in northern Afghanistan.
NATO said the operation took place Wednesday near Bala Murghab valley in Baghdis province.
In western Ghor province, U.S. military officials backed off on an earlier claim that a top insurgent commander was killed on Wednesday. Military officials initially reported that commander Mullah Mustafa was killed, along with 16 other militants, in an airstrike.
On Thursday, a military statement said "credible reports surfaced that Mustafa survived the attack." Ghor's deputy governor Keramuddin Rezazada said Mustafa was not killed. He also said villagers told him 10 civilians and 12 armed individuals were killed in the attack.
Officials said Mustafa commanded 100 fighters and reportedly had links to both the Taliban and the Iranian Revolutionary Guards.
Elsewhere in northern Afghanistan, the Defense Ministry said at least 12 militants and one Afghan soldier were killed in clashes throughout Baghlan province on Wednesday.
In southern Ghazni province, authorities said Taliban militants killed two police officers Wednesday. Elsewhere in Ghazni, police said at least one Afghan soldier was killed in a roadside bombing.
Some information for this report was provided by AFP, AP and Reuters.