The nation's largest transit agency has beefed up security as a precaution following the suicide bombing in Moscow's subway system.

A spokesman for New York's Metropolitan Transportation Authority, Kevin Ortiz, says the agency has a "heightened security presence" as a result. He declined further comment.

The agency is in charge of New York City buses and subways, as well as suburban trains, and bridges and tunnels.

Russian authorities say two female suicide bombers blew themselves up in Moscow on Monday in a subway jam-packed with rush-hour passengers, killing dozens.