AMMAN, Jordan -- Jordanian officials rounded up dozens of known Islamic extremists for questioning Tuesday in the assassination of American diplomat Laurence Foley as suspicion for the attack fell on al-Qaida or the terrorist movement's sympathizers.

A Jordanian official, speaking on condition of anonymity, said most of those detained were Jordanians of Palestinian origin who belonged to militant Islamic cells. Some were released but others were held for further questioning; none had been charged.

One militant, sought in an attack on a police station last year, was apprehended Tuesday after a shootout with police near the southern town of Maan.

He later escaped from a hospital but was not a suspect in Foley's assassination, officials said.

Foley, 60, an administrator at the U.S. Agency for International Development, was shot by a lone gunman at close range as he walked to his car in front of his home in Amman. The gunman escaped.

King Abdullah II and his wife, Queen Rania, visited the U.S. Embassy on Tuesday to sign a condolence book and meet briefly with Foley's widow, Virginia. In an interview with CNN, the king described the killers as "evil extremists" bent on harming Jordan and promised to bring them to justice.

Foley's slaying -- the first such targeted shooting of an American diplomat in decades -- stunned Amman's diplomatic and expatriate community, which had generally felt safe despite rising tensions in the Middle East.

Travel advisory issued

The U.S. Embassy advised Americans to "exercise caution" and vary their travel routes. Jordanian officials said additional guards and plainclothes police would be provided to Western diplomats.

Police and paramilitary units planned roadblocks on major thoroughfares, especially at night, a Jordanian security official said.