By Alexei Anishchuk and Barbara Lewis

BRUSSELS (Reuters) - Russian anger at an EU energy law blocked progress at talks between Russian President Vladimir Putin and European Union leaders on Friday.

Putin, on his first visit to Brussels since his re-election as president in May, was greeted by four topless women, protesting against civil rights curbs in Russia and shouting "Putin, go to hell". They were bundled away by police.

Relations between the 27-nation bloc and Russia, its main external supplier of energy and a key trading partner, have long been poisoned by rows over gas pipelines.

Europe relies on Russia to cover around a quarter of its natural gas needs, but over the past decade Moscow has had a series of disputes with its ex-Soviet neighbors - Ukraine and Belarus - that disrupted its gas exports to Europe.

Those disputes increased the EU's determination to diversify supply away from Russia.

Adding to the grievances are simmering trade disputes over everything from cars to pigs, and European leaders' condemnation of the jailing of members of the band Pussy Riot, seeing it as part of a trend of squashing personal freedoms.

For Russia, which sits on the world's largest natural gas reserves and supplies more than a quarter of the European Union's natural gas imports, energy is the major issue.

In opening comments, Putin referred to EU energy law as "uncivilized".

POTENTIAL

"Of course the EU has the right to take any decisions, but as I have mentioned ... we are stunned by the fact that this decision is given retroactive force," Putin told reporters on the sidelines of a Russia-EU summit in Brussels. "It is an absolutely uncivilized decision."

He was referring to EU legislation to create a single energy market and prevent those that control supply, such as Russia's Gazprom, also dominating distribution networks.

From the European Union side, European Commission President Jose Manuel Barroso said there was "huge potential for cooperation" to the benefit of both sides.

"I think we should in fact be able to transform what is today an interdependence by necessity into an interdependence by choice, a political choice," he said. "That's what requires political leadership on both sides."

Expectations for Friday's talks have always been low, but Russian and EU sources both see the need for continued dialogue.

The EU's executive Commission added to tensions between Europe and Moscow in September when it opened an investigation into suspected anti-competitive market practices by Russia's state-dominated Gazprom.

Trade disputes are also high on the agenda. EU Trade Commissioner Karel De Gucht said this month time was running out for Russia to settle trade disputes with the EU on everything from pigs to cars and he threatened to take Moscow to the WTO.

Putin also complained about lack of agreement on travel visas, saying Russia was being unfairly treated compared with other nations.

"I have a long list of states here with me which have a visa-free regime with the EU. There is Venezuela, Honduras, Mauritius, Mexico, seems everyone else is there," Putin said.

(Additional reporting by Adrian Croft and Justyna Pawlak)