Riyadh, Saudi Arabia ? Saudi Arabia issued the names and photos of its 26 most wanted terrorist suspects and increased protection around Western housing compounds in the capital Saturday as the United States upgraded its security warning, restricting its diplomats’ movements.

The new U.S. warning ordered embassy and consulate staff not to leave the heavily guarded diplomatic quarters in Riyadh and other cities, except for essential duties.

The steps came days after the United States and Britain warned that militants were scoping out Western residence complexes for a possible new terrorist attack after two suicide bombings on compounds that year that killed a total 52 people.

Separately, an American and a Briton have been detained by Saudi authorities in Jiddah, the U.S. and British embassies said Saturday, but embassy officials said they did not know the reason. A state-controlled newspaper identified the American as the brother of two people who have pleaded guilty in the United States to conspiring to help al-Qaida.

A U.S. diplomat declined to say if the new restrictions on diplomats’ movements were in response to a specific terrorist threat. Saudi security forces have strongly defended the Riyadh Diplomatic Quarter, an area of about five square miles west of the city, since suicide bombers attacked three housing compounds for foreigners in the capital on May 12.

The Saudi government on Saturday published the names and photographs of its 26 most wanted people, alleging they were “connected to the terrorist events in the kingdom over the past months.” The list had one Yemeni citizen, two Moroccans and 23 Saudis.

In a release aired on state television and released on the official Saudi Press Agency, the Interior Ministry said Saturday it was offering a reward of $267,000 to information leading to the arrest of one of the 26 wanted. The reward would rise to $1.3 million for information leading to the arrest of more than one wanted person, and to $1.9 million for actions that foil an attempted terrorist attack.

The Saudis launched a widespread crackdown on Islamic militants and al-Qaida cells after the May suicide bombings, which killed 35 people.