LONDON (Reuters) - British police carried out a controlled explosion on a suspicious item found on a London underground station on Thursday, and said counter-terrorism had launched an investigation into the incident.

Police were called shortly after 6 a.m. ET after rail staff reported finding the item on a train at North Greenwich underground station, near the Canary Wharf financial district and close to the O2 entertainment center.

A controlled detonation was carried out to make the item safe and officers from London's Counter Terrorism Command have taken the lead in the investigation, police said.

"We're keeping an open mind at the moment," a spokesman for the British Transport Police said, declining to give any further details about why police suspected a possible terrorism link.

Britain is on its second-highest alert level of "severe", meaning an attack is considered highly likely.

The Jubilee underground line was partially closed for more than four hours because of the incident, but North Greenwich station remained closed while more inquiries were carried out.

(Reporting by Michael Holden; editing by Stephen Addison)