JAKARTA The American Embassy was closed here on Thursday, and will remain so until further notice, because of a "security threat," the embassy announced on its Web site and in e-mail messages to American citizens early Thursday morning. It was the first time the American Embassy here had been closed for security reasons since September 2002, an embassy spokesman said. A senior counterterrorism official at another Western embassy and a private security analyst with close ties to Western intelligence agencies said the closing came after diagrams of the American Embassy were found on an Islamic Web site. The Web site, www.istimata.co.nr, had details of the floor plan where the ambassador has his office, including the location of cameras and thermal devices, the security analyst said. It went on to discuss methods of attack and suggested that the best would be a shoulder-fired weapon, he said. It said that a suicide bomber with a vest could not carry out the attack inside the embassy because he would have to pass through a metal detector and a thermal detector. It would be better to use a rocket-propelled grenade fired from the parking area into the ambassador's office, the group said. It also suggested mixing 150 kilograms, or 330 pounds, of TNT with Rodex, which would create a blast impact of 30 meters, or 100 feet. Rodex is a mixture of propane and oxygen used in killing rodents, which creates an underground bomb instantly, according to the company that manufactures it, Rodex Industries in Idaho. The American Embassy refused to provide any details about the nature of the threat or what it was based on, "because of a security threat - that's all I can say," said a spokesman for the embassy, Max Kwak. Separately, and unrelated to the closing of the embassy, Indonesia agencies have picked up telephone conversations in recent days suggesting that two of the most wanted terrorists in Southeast Asia, Azahari bin Husin and Noordin Mohammed Top, were planning attacks on several locations, Indonesian officials and the security analyst said. The two men were the masterminds behind the bombing of the Marriott Hotel and Australian Embassy last year, American, Australian and Indonesian officials have said. In spite of the embassy closing, counterterrorism officials say that the threat of a terrorist attack here has diminished here. Seeming to underscore this, the Jakarta International School, which most American students attend, and which has been a potential terrorist target in the past, remained open on Thursday, as did the American recreation club, where embassy personnel and their families swam and played tennis. It did not appear that other embassies had closed Thursday. The Australian and British embassies, which have been the most likely to close when there has been a generalized terrorist alert were open. The largest terrorist organization that has operated out of Indonesia, Jemaah Islamiyah, has been considerably weakened because of arrests and better intelligence by the Indonesian police, Western intelligence and law enforcement officials said in recent interviews. Since the Bali bombing in October 2002, which killed more than 200, the Australian and American governments have undertaken major training programs with the Indonesian police. Of greater concern than Indonesia is the Philippines, American, Australian and European officials say. Jemaah Islamiyah is still sending recruits there for training, they said. Husin and Top continue to elude capture. Last November, a special counterterrorism team was close to arresting the men when Police Chief Dai Bachtiar boasted to local reporters, and that sent the suspects into deeper hiding. They are alleged to have been the masterminds of the last bombing here, of the Australian Embassy last September.