Football star David Beckham spoke of his "heartbreak" as former club Manchester United and local rivals Manchester City came together Tuesday to pay tribute after 22 people including children were killed in a suspected suicide bombing in the northern English city.

Britain's deadliest terror attack in 12 years took place when a bomb went off shortly after the end of a concert by US pop star Ariana Grande at the Manchester Arena on Monday.

Former England captain Beckham, who made his name as a global superstar at United after coming through the club's youth system, expressed his condolences via an Instagram message, saying: "Heartbreaking news from Manchester. As a father & a human what has happened truly saddens me. My thoughts are with all of those that have been affected by this tragedy."

Gary Lineker, another former England international and now a television presenter, summed up a mood of widespread revulsion when he tweeted: "To target children at a concert is beyond comprehension. Beyond lunacy. Beyond evil. Heart goes out to all those who've lost loved ones."

A help centre was opened at City's Etihad Stadium for those affected by the blast, while the United club flag at their Old Trafford ground was flown at half mast.

Both Premier League clubs posted short statements Tuesday on their Twitter accounts, with United saying: "We are deeply shocked by last night's terrible events at the Manchester Arena. Our thoughts and prayers go out to all those affected."

Meanwhile, City said: "It's with great sadness we hear of the terrible events at the Arena. Our hearts go out to all affected and to our city's emergency services."

Current players from both clubs also sent Twitter messages of support, with City captain Vincent Kompany saying: "I would like to express my deepest condolences to the families of the victims. It's a sad day for the great city of Manchester. #Unity'."