LONDON — A homemade **** exploded on a packed London subway train during rush hour on Friday, leaving 22 people *******, ****** and health officials said. None of the ******* is thought to be seriously hurt.

****** say the ********* was a ********* ******, the fifth in ******* this year. *******’s domestic spy agency is helping out in the *************.

****** were alerted to an ******** at 8:20 a.m. local time after ********* reported a noise and a flash aboard the District Line train at Parsons Green station in the southwest of the city. ***** then ensued as hundreds of people rushed to get away from danger.

“I ended up squashed on the staircase, people were falling over, people fainting, crying, there were little kids clinging on to the back of me,” Ryan Barnett, 25, said of the “absolute *****” as people tried to leave the station.

Mark Rowley, head of counterterrorism for the Metropolitan ******, said “we now assess this was a detonation of an improvised ********* device.”

He said 18 people had been *******, most with “flash burns.” Health officials later said four others took themselves to hospital.

Rowley said the domestic intelligence service, MI5, was assisting with the *************, led by the ****** counter-********* unit.

He gave no information about potential suspects, saying “It’s very much a live *************.” Forensic officers combed the scene for clues and detectives examined surveillance camera footage in an attempt to get a glimpse at who planted the ****.

U.S. President ************ tweeted that it was another ****** “by a loser *********,” adding that “these are **** and demented people who were in the sights of Scotland Yard.”

The London ****** force declined to comment on *****’s suggestion that it knew about the ********.

Photos taken inside the train show a white plastic bucket inside a foil-lined shopping bag. Flames and what appear to be wires emerge from the top.

London ambulance service said they had sent multiple crews to the Parsons Green station and 18 people were hospitalized, though none had life-threatening ********.

“There was out of the corner of my eye a massive flash of flames that went up the side of the train,” eyewitness Chris Wildish told Sky News, then “an acrid chemical smell.”

He said many of those on board were schoolchildren, who were knocked around as the crowd surged away from the fireball.

Another commuter, Richard Aylmer-Hall, said he saw several people *******, apparently trampled as they fled what he described as a packed train.

At capacity, the train could hold more than 800 people.

“I saw crying women, there was lots of shouting and screaming, there was a bit of a crush on the stairs going down to the streets,” Aylmer-Hall, said.

Aerial footage later showed ********* from other subway trains being evacuated along the elevated track.

Transport for London said subway services were suspended along the line.

London Mayor Sadiq Khan said the city “utterly condemns the hideous individuals who attempt to use ****** to harm us and destroy our way of life.”

London has been targeted by ********* several times this year, with ****** vehicle ******* near Parliament, on London Bridge and near a mosque in Finsbury Park in north London. Beyond the capital, a May 22 ******* **** ****** at ********** Arena ****** 22 people.

The London Underground itself has been targeted several times in the past, notably in July 2005, when ******* bombers blew themselves up on three subway trains and a bus, ******* 52 people and themselves. Four more bombers tried a similar ****** two weeks later, but their devices failed to fully explode.

Last year Damon Smith, a student with an interest in ******* and Islamic extremism, left a knapsack filled with explosives and ball bearings on a London subway train. It failed to explode.

In its recent Inspire magazine, al-Qaida urged supporters to target trains.

Separately, French counterterrorism authorities were investigating an attempted knife ****** on a soldier patrolling a large Paris subway interchange.

The Paris prosecutor’s office says counterterrorism investigators have opened a probe into Friday morning’s ******** at the Chatelet station in central Paris, based on preliminary examination of the ********’s background.

The knife-wielding assailant tried to ****** a soldier with a special military force assigned to protect prominent sites following ****** Islamic extremist *******. He was quickly arrested and no one was hurt.