Security has been stepped up on the London Underground network, police said Saturday, following the arrest of a 19-year-old man after a suspicious item was discovered on a Tube train.

"The public will see more officers, including armed police, in and around transport hubs," a Scotland Yard spokesman told AFP.

Armed police arrested the 19-year-old in London on Friday under counter-terrorism laws in connection with the suspicious package found the day before.

An electric stun gun was used during the arrest on a busy shopping street, but no shots were fired.

The suspect, who was arrested on suspicion of the commission, preparation and instigation of terrorism acts, remains in custody on Saturday.

The item, found on a train at North Greenwich station, which serves the O2 entertainment complex in southeast London, was being forensically examined.

Britain's current national terror threat level has been set at severe -- the fourth-highest of five -- since August 2014, meaning an attack is considered highly likely.

The Times newspaper spoke of a "lone wolf" and said that the incident was "feared to be the first credible bombing attempt on the London transport network in more than 10 years".

Scotland Yard refused to comment on the report.