German Chancellor Angela Merkel said the West was imposing sanctions on Russia to stand up for international law and added that she would address the Sea of Azov issue with Russian President Vladimir Putin at an upcoming G20 summit.

"We don't impose sanctions on Russia for sanctions' sake, rather we impose sanctions to make clear that countries, even if their territorial situation puts them close to Russia, have the right to their own development," she told a Germany-Ukraine conference in Berlin. "Those are the principles of international law."

The European Union's hawks have called for more sanctions on Russia after a fresh flare-up of tensions with Ukraine but the divided bloc is not going to act swiftly if at all, diplomatic sources have said.

Merkel added that there is "no military solution" to the Ukraine conflict after Ukrainian President Petro Poroshenko asked for NATO naval support in his country's standoff with Russia. Blaming Russia for the tensions, Merkel said: "We ask the Ukrainian side too to be sensible because we know that we can only solve things through being reasonable and through dialogue because there is no military solution to these disputes." 

In interviews with Germany's Bild newspaper and the Funke newspaper group on Thursday, Poroshenko rejected Russia's charge that the vessels' entry into the Azov Sea was a provocation.

Two Ukrainian Azov Sea ports, Berdyansk and Mariupol, are effectively under blockade by Russia as vessels are being barred from leaving and entering, said Volodymyr Omelyan, Ukraine's infrastructure minister, on Thursday.

Overall, 35 vessels have been prevented from carrying out normal operations and only vessels moving towards Russian ports on the Azov Sea are permitted entry, he said on Facebook.

"The goal is simple - by placing a blockade on Ukrainian ports on the Azov Sea, Russia hopes to drive Ukraine out of our own territory - territory that is ours in accordance with all relevant international laws," he said.