Massive Attack have said they were “surprised and disappointed” by their treatment by Singaporean authorities after expressing pro-Palestine sentiments during a performance in the city-state.

The group wrote on Instagram on Sunday that its members were “detained by the police, isolated and separately questioned”, with some subject to hotel room searches and temporary passport confiscation.

The band’s two members held up a Palestinian flag during its 29 July show there and shouted “free Palestine” alongside members of the audience.

Singapore, which has stringent rules on public speech and assembly, subsequently said it had indefinitely banned Massive Attack from returning to the country.

A police spokeswoman told the BBC on Friday that the two band members would not be allowed to re-enter Singapore and were barred from performing there.

Robert Del Naja and Grant Marshall were “given stern warnings” concerning alleged offences under two laws that restrict the public display of foreign flags and regulate political expressions at public events.

Massive Attack said that before the show and again at the end “large sections of the auditorium organically led chants of ‘Free Palestine’, presumably aware but undeterred that this spontaneous expression alone could violate their government’s censorship laws”.

The band did not address the ban directly, but described the situation as a “surreal experience” and said they “did not imagine that merely holding up the flag of a sovereign state recognised by 157 countries would violate any law”.

They added that they were “proud to have made the impromptu expression” with fans in Singapore, who “clearly felt a moral imperative to show solidarity with the people of Palestine”.

Massive Attack are known for openly expressing their political stance on a range of issues, including the war in Gaza.

Del Naja was arrested earlier this year on suspicion of showing support for the proscribed organisation Palestine Action during a protest in London.

The 61-year-old sat among hundreds of fellow demonstrators with a sign that read “I Oppose Genocide, I Support Palestine Action”.

Singapore has taken a strong stance on public statements on the Israel-Gaza war, with authorities in the multicultural country insisting this was necessary to preserve racial and social harmony.

The home affairs ministry put out a statement in 2023 advising against “the public display and wearing of articles” in relation to the Israel-Gaza war, including foreign national emblems.

Massive Attack are currently on a world tour, with performances next week in Australia following the end of its Asia leg.

The BBC has contacted the Singaporean police for comment.