Nine American soldiers were killed and 15 wounded in the Taliban assault on a U.S. military base in northeast Afghanistan Sunday. That is the highest toll for an attack on U.S. forces in Afghanistan in three years. Scores of Taliban were killed as they were driven back, according to the North Atlantic Treaty Organization.

Some 200 Taliban fighters attacked the remote base in the mountainous region of Kunar. Lt. Col. Goetz Haffke, a NATO spokesman, said of the enemy: "This was the first time we had an attack in these huge numbers. They are attacking bases on a regular basis, but this was the first time we had such massive long-term fighting."

The attack shows the Taliban growing bolder and more aggressive in areas outside their original base in southern Afghanistan. It also reflected some local cooperation as the Taliban fighters fired on U.S. troops from houses and a mosque in a hamlet less than 30 miles from the mountainous border with Pakistan.

Militants have increased attacks near the capital of Kabul, which had been relatively quiet. They have been "terrorizing" Afghan officials and others who cooperate with the central government, the Wall Street Journal reports.

The Taliban's resurgence reflects its ability to rebuild its forces in Pakistan. It may also show that jihadists from other countries are targeting Afghanistan rather than Iraq.

Afghan President Hamid Karzai has stressed that Pakistan is at fault for allowing the Taliban a safe haven in its lawless regions. As Pakistan shirks its duty, the Taliban grows stronger, expanding its reach to former peaceful areas in Afghanistan.

U.S. commanders have indicated they need as many as three more brigades in Afghanistan or 10,000 additional troops to train Afghan forces and fight the insurgency. That should be done.

But the diplomatic challenge is clear: Washington must prevail on Islamabad to deny the Taliban sanctuary in Pakistan.