Update: Terrorist blast injures 22 during London's subway's rush hour

[LONDON] At least 22 people were injured when a suspected terrorist set off an improvised explosive device on a London subway train during the morning rush hour.

It is the fifth attack this year.

Police appealed for photos and information, and have identified one suspect connected with the blast.

Images of a small fire in a white bucket with protruding wires were broadcast by Sky News, which said the device had probably failed to detonate fully.

It may have had a timer, Sky reported. Parsons Green subway station in west London was cordoned off amid witness reports of a stampede as passengers had tried to flee the blast.

"My thoughts are with those injured at Parsons Green and emergency services who are responding bravely to this terrorist incident," Prime Minister Theresa May said on Twitter. May will chair an emergency meeting of officials.

US President Donald Trump said on Twitter that the "loser terrorist" was "in the sights of Scotland Yard," a reference to the headquarters of London's Metropolitan Police Service.

In an apparent US leak, CBS reported that the explosives were consistent with those used in another recent attack.

The US and UK have close intelligence-sharing ties and the UK has publicly criticized US leaks of police intelligence after previous attacks.

Londoners are growing used to terrorism and to the sight of heavily armed police patrolling the transport network.

The police have stepped up the number of arrests and Thursday reported that terrorism-related arrests had risen 68 per cent over the past year. The terror threat level is "severe," meaning an attack is likely.

The latest attempt comes after a series of attacks this year.

BLOOMBERG