Massive Attack have called being banned from Singapore a “surreal experience” after displaying a Palestinian flag during their show.

On Wednesday, the English trip-hop collective – whose current lineup includes Robert “3D” Del Naja and Grant “Daddy G” Marshall – played a show at the Star theatre.

After unfurling and displaying a Palestinian flag while performing, they became the subject of a police investigation, which led to them being banned from the country.

Singapore, known for its tough laws on public speech and assembly, bans the open display of all foreign flags, national emblems or banners without a permit.

On Sunday the band issued a statement on Instagram. “Following our performance at the Star Theatre, Singapore, on 29th July, we were surprised and disappointed that our entire band was detained by the police, isolated and separately questioned – with some members subjected to hotel room searches and temporary passport confiscation,” it read.

“Before we set foot on the stage and again at the end of the show, 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.

“For our part, we did not imagine that merely holding up the flag of a sovereign state recognised by 157 countries would violate any law.”

The statement continued: “On reflection, we are proud to have made this impromptu expression with our fans in Singapore who clearly felt a moral imperative to show solidarity with the people of Palestine in their ongoing reality of illegal occupation, apartheid and genocide, and we salute their courage in doing so. Right across the world, the continued inaction of the ‘international community’ is moving citizens to personal risk.”

The band said the “surreal experience” was a “reminder of the importance of defending universal human rights and freedom of expression, wherever those rights are threatened”.

They added: “At home in the UK peaceful protestors [are being] arrested under terrorism laws for holding up handwritten signs protesting genocide, despite appeals from all sides of the political spectrum.”

Concluding the statement, Massive Attack said: “We are grateful to the people of Singapore who made us feel so welcome, and hope that the Government of Singapore will choose to ratify the UN International Covenant on Civil and Political Rights and allow their citizens expressions of conscience without fear of state prosecution. As we were saying … Free Palestine.”

A statement released on Saturday by the Singapore police force and the Infocomm Media Development Authority said police had investigated both Del Naja and Marshall for “their actions of support for a political cause and unfurling of a foreign flag”.

The authorities said that after an investigation, which included consultation with the attorney general’s chambers, police had issued “stern warnings” to both men for allegedly breaching the Foreign National Emblems (Control of Display) Act and the Public Order Act.

The statement said both men would “also be banned from re-entering Singapore” while any future applications for them to perform there would not be approved.

Police “take a serious view of acts which could potentially harm the racial and religious harmony in Singapore and urge the public, including foreigners, to refrain from importing foreign politics as this can undermine our social cohesion and the rule of law”.

Del Naja was among 500 people arrested in April during a demonstration in London against the ban on Palestine Action, a group that has been proscribed in the UK.

The Singapore police force has been contacted for comment.