The United States closed its consulate in the Nigerian city of Lagos (search) after receiving a "terrorist threat" by telephone, a U.S. military official said Friday. The move prompted Britain, Germany, Italy and Russia to close their nearby diplomatic missions.

The closure of the American mission began Thursday afternoon after "there was some kind of terrorist threat made," U.S. Maj. Holly Silkman, a spokeswoman for the Germany-based U.S. European Command (search), told reporters in Dakar, Senegal.

The threat was "called in," she said without elaborating.

Silkman was in Dakar for U.S.-led counterterrorism exercises involving Nigeria (search), Senegal and seven other African nations.

Nigerian authorities are working with the United States in the investigation, Nigeria's Foreign Ministry said in a statement.

About 100 armed police patrolled the Lagos street where the U.S. consulate and several other diplomatic missions are located, with some searching cars for explosives.

A Nigerian police bomb-disposal squad brought its van to the area Friday, and American-employed security guards stood outside the consulate and patrolled in cars.

All diplomatic missions on the street bordering a lagoon were closed. British officials said they were responding to the U.S. move and hoped to reopen Monday.

The U.S. Consulate will reopen Monday, U.S. Embassy spokesman Rudolph Stewart said from the capital, Abuja.

Asked whether that meant the threat was over, he said: "No, it hasn't abated. We just felt that we can't stay closed forever."

Nigerian police spokesman Emmanuel Ighodalo later played down the threat, saying police only mobilized because it was "a request made by the embassy."

"We had to satisfy them," he said. "I don't think there's any specific threat."

The closure came amid the U.S.-led counterterrorism exercise that was part of efforts to improve regional collaboration against terror threats.

Al-Qaida chief Osama bin Laden purportedly targeted Nigeria in an Internet statement posted last year. The country of about 130 million people is about evenly split between Christians and Muslims.

Political, ethnic and religious violence has claimed more than 10,000 lives since President Olusegun Obasanjo won came to power in a 1999 election, but the country has not experienced any terrorist bombings.