ACIA drone strike has killed Anwar al-Awlaki, one of the world's most wanted terrorists. Awlaki's death is another blow to al-Qaida, and proof yet again of the extraordinary reach bestowed on the United States by its technology.

But this killing exposes two dilemmas for the U.S.: First ,the operation was based on close cooperation with Yemen, a government headed by President Ali Abdullah Saleh, whom Washington has publicly called on to leave office as demanded by prodemocracy activists. Second, the killing raises troubling moral and legal questions — Awlaki carried a U.S. passport and U.S. law prevents the killing of its own citizens without due process.

Awlaki was on the most wanted list for several years. The U.S. tried and failed to kill him in a missile attack in southern Yemen last May. He retreated to a mountainous region in another part of the country and cut himself off from all electronic communications, but Yemeni intelligence services tracked him down, surveilling him for weeks until the U.S. launched a second successful strike against a multicar convoy last Friday.