MANILA Militants may have planned to bomb the U.S. Embassy in Manila simultaneously with the terror attacks in New York and Washington earlier this week, Philippine officials said on Friday.

Three men, all nationals from Oman, were taken in for questioning in the city last week after they were found video-taping the sprawling U.S. Embassy, which occupies a large area fronting Manila Bay, police Intelligence Director Robert Delfin told Reuters.

There was no evidence to hold them further, and the three left for Thailand on Sunday, Delfin said. But a later routine search of their room at the bay view hotel, which is opposite the embassy, indicated residue of bomb-making material, he said.

By that time the three had left for Bangkok.

"The initial feeling is they may have planned to attack the embassy before September 11 or on September 11," presidential palace spokesman Rigoberto Tiglao told Reuters.

That was the day hijacked planes were flown into the world trade center in New York and the Pentagon in Washington. U.S. officials have said the hijackers were probably men of Middle East origin and that Saudi-born exile Osama bin Laden was a key suspect in the conspiracy.

Tiglao said the name of one of the three men questioned in Manila also appeared on the manifest of one of the American Airlines planes hijacked in the United States, but it could be a common Arab name. Further investigations were under way, he added.

"They were suspicious-looking," Delfin, the Philippine police officer, said of the three Omani men. "They took pictures of the embassy and were accosted by police...no arrests, but they left the country two days later.

The search of their hotel room "was positive for the chemicals that could be used in a bomb...residue of bomb-making materials," he added.

*****Joint U.S.-Philippine Operations*****

President Gloria Macapagal Arroyo told reporters in Tokyo earlier on Friday that joint operations between the Philippine police and U.S. authorities were being held at the bay view hotel.

National security adviser Roilo Golez said the operation at the bay view was aimed only at securing the area and preventing any threat to the U.S. Embassy.

"It's just for security," he told Reuters. "It (the building) is fronting the embassy. You could have snipers there."

Asked if there was now any specific threat to the embassy in Manila, Golez said there was not, but added: "We presume there is a threat worldwide."

Japanese media quoted Arroyo as saying on Thursday that there might be a connection between those who Planned and carried out the acts of terror against the United States and fundamentalist Abu Sayyaf guerrillas in the Philippines.

Both groups profess to fight for an Islamic state but the Abu Sayyaf, holding a U.S. missionary couple and 16 Filipinos hostage for 15 weeks on Basilan Island, is seen largely as a bandit group whose main business is kidnap for ransom.

The military never presented evidence to back up its claim. But the Abu Sayyaf has several times demanded the release of Islamic militants convicted in the 1993 plot to blow up the world trade center in exchange for freeing its hostages.