The State Department and the United Nations are tightening security at their outposts in Pakistan and throughout Central Asia after receiving warnings that Islamic militants with links to Osama bin Laden may be planning attacks in the region, U.S. and U.N. officials said today.

An internal memo circulated by the office of the U.N.'s security coordinator, Benon Sevan of Cyprus, cited "reliable reports" that supporters of the Saudi militant might attack U.S. or U.N. targets in Pakistan, Afghanistan, Uzbekistan, Tajikistan, Kazakhstan or Turkmenistan in retaliation for trade sanctions imposed by the U.N. against Afghanistan.

"We have good information that U.S. and U.N. interests could be attacked by supporters of bin Laden," a U.N. staff member told senior officials at a security briefing Monday, according to a participant in the closed-door meeting.

Bin Laden, who is living in Afghanistan under the protection of its ruling Taliban militia, has been indicted by a New York grand jury on charges of conspiracy and murder in the August 1998 bombing of U.S. embassies in Kenya and Tanzania, which killed more than 220 people. The United States has offered a $5 million reward for information leading to his arrest.

Trade sanctions went into effect last week after the Taliban refused to expel bin Laden. The sanctions, which call on U.N. members to freeze the Taliban's foreign assets and bar all flights by the Taliban's airline, were approved by a unanimous vote of the U.N. Security Council's 15 member nations, including China and Russia.

While the memo and the briefing provided no details on the source of the warnings, officials said Sevan's office was taking them seriously enough to place U.N. relief workers in the region on alert and to hold down their numbers. There are now about 40 U.N. relief workers in Afghanistan.

On Nov. 12, the State Department also reminded U.S. embassies around the world that sanctions against the Taliban were going into effect and urged all posts to "review their security situation and take additional measures if necessary," according to a State Department spokesman.

That day, militants fired rocket-propelled grenades at the U.S. Embassy and the U.N.'s local headquarters in Islamabad, the Pakistani capital. Protesters subsequently attacked several U.N. facilities in Afghanistan, including an office in the town of Farah that was burned to the ground.

Last week, however, the Taliban's leader, Mohammad Omar, appealed to the Afghan public to halt the demonstrations against the United Nations. The U.N., in turn, began to consider increasing its relief work. "What we might need to do is freeze that," a U.N. official said today. "The U.N. staff members in Afghanistan were resuming normal duty. Then we get this memo."