ISLAMABAD — As the U.S. looks ahead to its phased withdrawal from Afghanistan, even more attention is being directed toward Pakistan, where Obama administration officials say al-Qaida and its allies are still plotting attacks against the West.

They argue that threat has been effectively neutralized in Afghanistan, a key justification for President Barack Obama’s announcement Wednesday that the U.S. will withdraw 33,000 troops from Afghanistan by next summer. The U.S. invaded Afghanistan in 2001 because al-Qaida used it as the base to launch the 9/11 attacks.

Afghanistan could take on new significance for the U.S. as a base to launch unilateral strikes against militants inside neighboring Pakistan, an unstable nuclear-armed country that many analysts say is more strategically important than Afghanistan.

That future has become more likely as the relationship between Pakistan and the U.S. has deteriorated following the American raid that killed al-Qaida chief Osama bin Laden not far from the Pakistani capital last month. The operation humiliated Pakistan, which cut back on counterterrorism cooperation with the U.S., a popular move in a country where anti-American sentiment is rife.

“We haven’t seen a terrorist threat emanating from Afghanistan for the past seven or eight years,” said a senior administration official in a briefing given to reporters in Washington before Obama’s speech. “The threat has come from Pakistan over the past half-dozen years or so, and longer.”

One of the most high-profile attempted attacks against the U.S. homeland coming from Pakistan recently was by Faisal Shahzad, a Pakistani-American who tried to set off a car bomb in New York’s Times Square last year. He allegedly traveled to Pakistan’s tribal areas and coordinated his attack with the Pakistani Taliban.

Since Pakistan effectively prohibits American troops inside the country and has been a reluctant ally in targeting militants the U.S. deems a threat, Washington has increasingly relied on covert CIA drone missile strikes to target al-Qaida and Taliban fighters holed up in Pakistan’s mountainous border region with Afghanistan.