A 21,000-strong NATO-led force will assume responsibility for security over all Afghanistan by November, absorbing U.S. troops already deployed in the country's volatile eastern region, NATO's supreme commander said Monday. U.S. General James Jones said the NATO-led International Security Assistance Force (ISAF) will add the U.S. forces in the east after it completes its current expansion into southern Afghanistan. The move will shift responsibility for overall security in Afghanistan from the United States to NATO. "It is arguably NATO's most ambitious operation, perhaps in its history; certainly a strategic distance that is very impressive," Jones told reporters in Washington. "At the end of the day, when ISAF takes over in Afghanistan, it will be roughly a 21,000-man force from 36 different nations." The transition comes amid increasing attacks in Afghanistan and other signs of a resurgence of Taliban and al Qaida activity in the country. Jones said "more attacks, more testing" are expected this spring, particularly as ISAF moves into the south, but he said the Taliban and al Qaida are not strong enough to mount a major insurgency.