Updated

The Obama administration was preparing a request on Friday to block a lawsuit over the scope of its targeted killing program for suspected terrorists, in a case that challenges the government's powers in its war on terror.

U.S. officials say national security is threatened by Yemeni-American Islamist cleric Anwar al-Awlaki, whose fiery sermons are a major draw for anti-American jihadists on the Internet. Mr. Awlaki, a U.S. citizen, is believed to be targeted for extrajudicial killing for his alleged involvement in terror plots against the U.S.

A terrorism task force led by the Federal Bureau of Investigation in San Diego for years has been building a case against Mr. Awlaki, according to people familiar with the matter. Obama administration officials have recently weighed whether to bring an indictment against him, these people say.

Last month, Mr. Awlaki's father, with the aid of U.S. civil-liberties groups, filed suit in District of Columbia federal court seeking an order to stop the government from killing Mr. Awlaki unless he posed an immediate threat. The suit also asked the court to force the government to disclose the process it used to determine that a U.S. citizen can be executed without trial.

The government was scheduled to file its response to the suit late Friday. A U.S. official said the government would challenge Nasser al-Awlaki's standing to bring the suit on behalf of his son, who is believed to be hiding in Yemen. The government doesn't admit or deny whether it plans to kill Mr. Awlaki, or disclose any details of the targeted killing program. But the official said it would argue that Mr. Awlaki, as a U.S. citizen, would have access to the courts if he wants to surrender peacefully.

The filing was set to argue that it is not for the courts to decide whether it is legal to kill an American in Yemen, far from the actual battlefield in Afghanistan, where the U.S. is fighting al Qaeda. Congress and the president should determine that question, according to the filing.

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