WASHINGTON — An airliner escorted by military jets has landed at JFK airport.

The escort followed the discovery of a package containing explosive materials that was intercepted in Dubai on its way from Yemen to a Chicago Jewish institution. Meanwhile, authorities in London were investigating a suspicious package in England as part of a terror probe that spanned three continents, officials said today.

U.S. officials said they were increasingly confident the packages were part of a plot by Yemen's al-Qaida branch, the same group responsible for an attempted bombing of a U.S.-bound airliner last Christmas.

Intelligence officials have been monitoring the suspected plot for days, an official said. The packages were discovered in England and Dubai late Thursday after a foreign intelligence service picked up information related to Yemen and passed it on to the U.S., one official said.

An official United Arab Emirates security source said the package discovered there was a device containing explosive materials.

No explosives have been found in the U.S. Items continued to be tested in England.