The Japanese government on Thursday began tightening security across the country to prevent possible terrorist attacks on Japanese and American interests as a U.S.-led attack on Iraq began.

The National Police Agency (NPA) set up an emergency terrorism task force, beefing up security near U.S.-related facilities and some 650 key infrastructure facilities, including nuclear power plants and airports.

In the largest security measures ever taken to counter possible terrorist attacks, the agency also ordered police forces around the country to tighten security not just at landmark facilities but at places where people congregate in large numbers.

It also ordered police to work closely with immigration authorities and reinforce patrols along coastlines to prevent terrorist incursions, while intensifying exchanges of intelligence with concerned agencies of other governments.

''We have received no information pointing to a concrete terrorist threat,'' a police agency official said.

The Public Management, Home Affairs, Posts and Telecommunications Ministry decided to reinforce checks on whether bacteria and viruses such as anthrax may be attached to or enclosed inside postal mail.

The Metropolitan Police Department on the same day set up a command office to deal with security threats, deploying 5,000 officers to guard possible targets, including the U.S. military's Yokota base and the U.S. Embassy in Tokyo.

The Defense Agency said it is prepared to immediately deploy 2,700 troops and antiterrorist equipment such as a chemical protective vehicle of the Ground Self-Defense Force.

To counter possible attacks on the more than 50 nuclear reactors operating in the country, the industry minister asked his colleagues to order police and the Japan Coast Guard (JCG) to guard them.

Economy, Trade and Industry Minister Takeo Hiranuma told a press conference that he would ask 16 companies, including power producers, to strengthen security measures at their facilities.

Accordingly, the Nuclear and Industry Safety Agency issued measures to energy operators, including gas firms, power firms and petrochemical industry complex firms, to tighten security.

The JCG decided to increase its alert at nuclear reactors, U.S. military bases, airports and oil stockpiling bases on the seaside as well as at ports and harbors, covering some 140 areas nationwide, using patrol boats and aircraft.

In addition, the coast guard and the Land, Infrastructure and Transport Ministry's maritime department notified ship owners associations and marine transport organizations to inform them of locations of Japanese vessels.

At a separate news conference, Finance Minister Masajuro Shiokawa said he has ordered customs officials to check cargo shipments more carefully to prevent smuggling of firearms and explosives and asked financial institutions to make sure funds do not make their way into terrorists' hands.

Justice Minister Mayumi Moriyama said the same day that she has ordered immigration officials to tighten controls to prevent terrorists from entering Japan and called on authorities to strengthen patrols at international airports in the country.

Meanwhile, Health, Labor and Welfare Minister Chikara Sakaguchi said the ministry is expediting measures to counter biological and chemical weapons, although remarking that the possibility of their use in terrorist attacks in Japan is remote.

Separately, Environment Minister Shunichi Suzuki said his ministry will beef up controls on chemicals at the National Institute for Environmental Studies in Tsukuba, Ibaraki Prefecture, and the National Institute for Minamata Disease in Minamata, Kumamoto Prefecture.

The Foreign Ministry said it has activated its crisis management office to collect information on the U.S.-led war on Iraq and to secure the safety of Japanese nationals in Iraq and neighboring countries.

The office, manned by some 60 ministry officials and headed by Foreign Minister Yoriko Kawaguchi, will gather information on the war and will serve as a liaison for other ministries and Japanese overseas establishments, the ministry said.

Railway firms across the nation have also taken measures to step up patrols at stations and on railroad tracks.