About 500 anti-Kremlin activists have met in Moscow to discuss forming a movement called "Solidarity" in the latest bid to unite Russia's liberals against what they call growing authoritarianism.

Sunday's meeting came two days after Russian politicians approved constitutional amendments extending presidential terms from four years to six.

The amendments, critics say, could  facilitate the return of Vladimir Putin, the Russian prime minister, to the presidency.

The meeting, which nominated delegates for a founding congress of the new Solidarity movement scheduled for December 12-13, was attended among others by Garry Kasparov, the former world chess champion.

Activists in the new movement vowed to fight the amendments, which would become the first changes to Russia's post-Soviet constitution if they pass the upper house and two-thirds of regional assemblies, as widely expected.

"We will be one of the only political movements in Russia to stand in defence of the constitution," Ilya Yashin, one of the activists at the meeting, said.

Opposition unity

Yashin said that the founders of Solidarity had chosen the name in part because of the 1980s Polish trade union federation of the same name, which pushed the government of the Soviet bloc country to hold free elections in 1989.

"The victory of our Polish colleagues did much to inspire us," Yashin said.

Like the original Solidarity, the new movement plans to push for greater democracy, Yashin said, complaining that "there are no real elections in the country".

Previous attempts to unify the Russian opposition have stumbled due to disagreements over strategy and personal conflict between opposition leaders.