(AP) - New York City's transit agency says it hasincreased police presence at "key locations" in light of anongoing terror probe.

The Metropolitan Transportation Authority says there's nocredible threat to the city's subway system and commuter trains.But extra officers - with helmets and bulletproof vests - were seenat spots like Grand Central Terminal in midtown Manhattan.

Police Commissioner Raymond Kelly refused to comment on theterror probe that led to a nationwide terror warning Tuesday forentertainment complexes, sports stadiums and hotels. Three people,including a Queens imam, are charged with lying to officialsinvestigating the alleged plot.

Kelly says the city is "obligated" to put itself on heightenedalert whenever possible plots surface following the Sept. 11, 2001,and 1993 attacks at the World Trade Center.