UNITED NATIONS — The presidents of Afghanistan and Pakistan clashed yesterday at the United Nations over which nation is to blame for the growing violence in Afghanistan, each saying the other must do more to defeat the Taliban and Al Qaeda.

“We must look beyond Afghanistan to the sources of terrorism,” President Karzai of Afghanistan said in a speech to the General Assembly, without mentioning neighboring Pakistan, where suspected Al Qaeda operatives have been found in hiding.

“We must destroy terrorism sanctuaries beyond Afghanistan, dismantle the elaborate networks in the region that recruit, indoctrinate, train, finance, and deploy terrorists,” he added.

Mr. Karzai, 48, said growing violence inside Afghanistan prevented 200,000 children who went to school last year from resuming their educations this month and contributed to an increase in polio cases.The scope of rebel resistance has raised concern among countries contributing to an anti-terrorism force in Afghanistan about the prospects for restoring order.

President Musharraf of Pakistan took issue with Mr. Karzai’s view of the situation, saying his government is pursuing a “massive, multipronged” political and military strategy to assist Afghanistan. He said Pakistani tribal leaders this week adhered to their recent agreement with the government by turning over 10 Taliban members who had crossed the border from Afghanistan.

“Instead of this blame game that goes on, he must realize what is the correct environment and take action accordingly,” General Musharraf, 63, told reporters, referring to Mr. Karzai. “The problem lies in Afghanistan.”

The Pakistani leader said that, while some Taliban and Al Qaeda supporters have crossed the border from Pakistan, the Taliban leader, Mullah Omar, is in the Kandahar area of southern Afghanistan, and Mr. Karzai should go after him there.

“Military action is required against him and his commanders,” General Musharraf said. “Who is leading the Taliban? They are the same people who took over in 1995. They are the people of Afghanistan.”

General Musharraf’s statement came a day after a British official said some NATO nations doubt the alliance’s mission in Afghanistan can succeed and that talks over increasing the size of their deployment are “difficult.”

NATO forces in the past seven weeks have engaged in some of the fiercest fighting in Afghanistan since the 2001 ouster of the Taliban government, prompting calls from military commanders for more soldiers. A September 13 meeting of the alliance ended without pledges for more troops, though Poland has since offered 950 soldiers.

NATO forces based in the south this month battled Taliban rebels in Kandahar, reportedly killing more than 500 insurgents in just more than two weeks. While the international force said two days ago it had “successfully cleared” insurgents from Panjwayi, the focus of the operation, a suicide bomber in the district on September 18 killed four Canadian soldiers and wounded 25 locals.

“There’s no denying it has been difficult, and we’re not there yet,” British Defense Secretary Des Browne said in a speech in London at the Royal United Services Institute, a defense policy organization. “Some have doubts that the mission will succeed. Others, candidly, have more direct concerns about the level of risk they are prepared to submit their soldiers to.”

Still, Mr. Karzai said his government has met “all milestones” toward Afghanistan’s postwar transition, including a doubling of the nation’s per capita income since 2002.