Pakistan's powerful army chief has canceled a Monday visit to Britain as U.S. outrage grows over allegations that Pakistani spies helped insurgents attack American targets in Afghanistan.

Britain's Ministry of Defense said Gen. Ashfaq Pervez Kayani, who was expected to meet privately with U.K. Defense Minister Liam Fox, had canceled. It declined to speculate on why the visit was scrapped.

A Pakistani official said Kayani was staying in Pakistan to hold talks on the crisis sparked by the U.S. accusations against Pakistan's military-run Inter-Services Intelligence spy agency. The official spoke on condition of anonymity because of the sensitivity of the situation.

Last week, the chairman of the U.S. Joint Chiefs of Staff, Adm. Mike Mullen, accused the ISI of having backed an Afghan insurgent group in the planning and execution of a Sept. 13 assault on the U.S. Embassy in Afghanistan as well as a truck bomb that wounded 77 American soldiers days earlier.

Kayani, widely considered the most powerful man in Pakistan, has dismissed the allegations as baseless.

But a Republican on the Senate Armed Services Committee has said the U.S. should consider military action as an option against Pakistan if it continues to support terrorist attacks against Americans in Afghanistan.

Sen. Lindsey Graham also said assistance to Pakistan should be reconfigured, and that the U.S. should no longer designate an amount of aid for Pakistan but have a more "transactional relationship" with the country.