Faisal Shahzad, of Shelton, Conn., pleaded guilty in federal court in Manhattan to a 10-count indictment that included charges of conspiracy to use a weapon of mass destruction, attempting an act of terrorism and transportation of an explosive. He faces life in prison when he is sentenced.

Mr. Shahzad is one of a number of home-grown U.S. terrorists who have surfaced over the past two years, posing greater difficulties for antiterrorism officials to track than foreign-born suspects. Mr. Shahzad had no history of support for jihad and had not appeared on the government's radar, even though he received terror training in Pakistan late last year.

His case came six months after the deadly shooting rampage at Fort Hood in Texas in November, in which 13 soldiers were killed, allegedly by Army Maj. Nidal Hasan, an American-born Muslim of Palestinian descent who opposed U.S. military efforts in Iraq and Afghanistan. In another recent case, five American students from the Washington, D.C., suburbs were arrested in Pakistan in December after they allegedly developed contacts with al Qaeda via the Internet and tried to go to Pakistan to join a militant-training camp.

Mr. Shahzad, 30 years old, told the courtroom he would plead guilty "100 times over" until the U.S. pulls its troops from Afghanistan and Pakistan and stops unmanned drone strikes against terror suspects. "I am part of the answer to the U.S. terrorizing the Muslim nations and the Muslim people, and on behalf of that, I'm avenging the attacks," Mr. Shahzad said.