Us President George W. Bush's administration, concerned that a wave of attacks overseas could spread to the country, raised the terrorism alert level yesterday and called for increased security nationwide.

　　Authorities described the intelligence pointing to a domestic attack as general in nature, with nothing credible suggesting a time, location, method or target. They pointed to last week's bombings in Saudi Arabia and Morocco as part of a coordinated series that could spread.

　　"The intelligence community believes that al-Qaida has entered an operational period worldwide, and this may include attacks in the United States," US Homeland Security Secretary Tom Ridge said on Tuesday.

　　Ridge warned of attacks similar to those in Riyadh, Saudi Arabia, where gunmen fought with guards before suicide bombers detonated truck bombs at several lightly defended residential complexes.

　　US state and local authorities began reacting after Tuesday's announcement. Police in California began working 12-hour shifts. National Guard troops in New York were called up to protect subways and bridges. In Washington, the Capitol police SWAT team prepared to conduct random patrols.

　　The decision to raise the national alert to orange, signifying a "high" risk of attacks, from yellow, meaning an "elevated" risk, came after a review of intelligence information by US President George W. Bush's homeland security council on Tuesday, White House spokesman Ari Fleischer said. Orange is the second-highest on the five-color alert scale.

　　Ridge encouraged governors and mayors to deploy extra police and take other precautions, particularly at large public gatherings during the upcoming Memorial Day weekend.

　　Overseas, US officials also took additional security measures. The United States, Britain and Germany temporarily closed their embassies and consulates in Saudi Arabia on Tuesday following warnings.

　　The US Federal Aviation Administration is planning to temporarily prohibit flights over sports stadiums and restrict small private planes flying within a 27.75-kilometer radius of the Washington Monument, said agency spokeswoman Laura Brown.

　　The FAA also will require private planes flying into three Washington-area airports to first land at Tipton Airport in Maryland so the pilots can be checked, Brown said.

　　A Saudi official said dozens of Muslim militants linked to al-Qaida were believed ready to volunteer for suicide bombings like the ones in Riyadh.