Moscow police say they detained five activists from human rights group Amnesty International who were handing out leaflets to the audience before a concert by U2.

Police spokeswoman Zhanna Ozhimina said Thursday (Aug. 26) the activists were detained because they did not have the necessary authorization. They were released after a few hours.

The activists were handing out leaflets and urging concert-goers to sign petitions pressing Russian authorities to bring to justice the murderers of journalist Anna Politkovskaya and rights activist Natalya Estemirova.

The head of the rights group's Moscow office, Sergei Nikitin, said U2 management had assured them before Wednesday's (Aug. 25) show that all the necessary permits were in place.

Russian police routinely break up protest actions.