Irish rappers Kneecap have denied supporting Hamas and Hezbollah and apologised to the families of murdered British politicians as a fierce row rages over political messaging at the band's concerts.

The denial, issued late Monday on social media, came after UK police said it was examining footage from a Kneecap concert last year that appeared to show a band member shouting "up Hamas, up Hezbollah".

Both groups are banned as terrorist organisations in the UK and it is a crime to express support for them.

Irish Prime Minister Micheal Martin urged the band to clarify whether they supported the groups or not.

"Let us be unequivocal: we do not, and have never, supported Hamas or Hezbollah," said the band's statement on Monday.

"We condemn all attacks on civilians, always".

UK police also said it was examining a video clip of the Belfast rap trio at a 2023 gig appearing to show one member saying: "The only good Tory is a dead Tory. Kill your local MP."

The family of Conservative MP David Amess, who was fatally stabbed by an Islamic State group follower in 2021, called for an apology from Kneecap.

The Belfast-based trio said in a statement on its Instagram channel, they "reject any suggestion that we would seek to incite violence against any MP or individual. Ever."

"An extract of footage, deliberately taken out of context, is now being exploited and weaponised, as if it were a call for action," said the statement.

"To the Amess and Cox families, we send our heartfelt apologies, we never intended to cause you hurt," it said, also referring to Labour MP Jo Cox who was murdered in 2016 by a neo-Nazi sympathiser a week before the divisive Brexit referendum.

But a Downing Street spokesman said he believed the group "should apologise".

"You've seen what they've said. I think it is half hearted. As you say, we completely reject in the strongest possible terms, the comments that they've made," he added.

Kneecap has also courted criticism during an ongoing tour due to its hardline anti-Israel messaging during gigs.

Sharon Osborne, a British television presenter, urged the revocation of their US work visas after their performance at California's Coachella on April 18, slamming their statements as "aggressive".

Messages displayed on a screen behind the band as it performed included "Fuck Israel. Free Palestine" and "Israel is committing genocide against the Palestinian people."

The war in Gaza followed an attack in Israel by Hamas militants on October 7, 2023, which resulted in the deaths of 1,218 people, mostly civilians, according to an AFP tally based on official Israeli figures.

Israel's military response in Gaza has caused a humanitarian crisis and killed at least 52,365 people, mainly civilians, according to the Hamas-run territory's health ministry.