Berlin  - German chancellor Angela Merkel will urge Russian President Dmitry Medvedev to take action on the situation of human rights activists in the Caucasus at a summit in Sochi on Friday.

Merkel told a German radio station on Thursday evening that she "knows Mevedev is serious about questions of human rights" - but that credible investigations now had to be conducted into the recent murders of three activists in Chechnya.

Zarema Sadulayeva, a prominent Chechen rights activist and her husband Alik Djibralov, were found shot dead near Grozny on Tuesday. The recent murders come less than a month after that of Natalya Estemirova, also in Chechnya.

The issue of human rights threatens to overshadow the long-planned summit between the two leaders, which had been scheduled to deal with mainly economic matters.

Russia is the EU's third-largest trading partner. Within the EU Germany is often seen as having the most leverage with Moscow, as Berlin has maintained a relatively pro-Russian stance in comparison with other EU partners - not least because of its heavy dependence on Russian gas supplies.

Energy relations between the EU and Russia, the possible sale of Opel to a consortium including a Russian bank, and preparations for the G20 summit to take place in the US in September will also be on the agenda, government spokesmen in Berlin have said.

Merkel is due to meet Medvedev in the Black Sea resort, which is to host the Winter Olympics in 2014, at around midday. (dpa)