MOSCOW -- Moscow police have detained four activists and a reporter over a brief protest in support of jailed opposition leader Aleksei Navalny held on Red Square.

Sergei Lukashov, Svetlana Lukashova, Sergei Rednikov, and Ilya Yermakov were detained on September 15, seconds after they unfolded a large banner saying "Free Navalny! Putin, go to jail," and chanting "Free Aleksei Navalny!"

Yevgeny Yevsyukov, who recorded the protest on video, was also detained. The OVD-Info human rights group said police confiscated Yevsyukov's journalist ID and beat Yermakov.

An ambulance was called to treat Yermakov, it said.

The protest was held as Russia prepares for elections on September 17-19.

In response to opposition efforts to loosen the hold of the ruling, Kremlin-backed United Russia party, the authorities have unleashed a sweeping crackdown against Navalny's allies and supporters, as well as the independent media, in recent months.

Navalny, who is Putin's most vocal domestic critic, is serving a 2 1/2-year jail sentence for parole violations for a conviction he says was trumped-up. His foundation has been designated an "extremist" organization.

His jailing has strained Moscow's relations with the West, which has demanded that he be freed and has criticized the "extremist" label.