Angela Merkel, the German chancellor, on Thursday declined to come to Ukraine's aid after its president appealed for help to block Russian aggression.

Petro Poroshenko, the Ukrainian president, appealed to Nato on Thursday, asking for naval support in the standoff with Russia and accused the neighboring state of wanting to annex the Sea of Azov.

Speaking to German newspaper Bild, Mr Poroshenko called Germany one of Ukraine's “closest allies” and urged it - together with other Nato countries - to deploy naval ships to aid his country after Russia fired on and seized three Ukrainian vessels near Crimea on Sunday.

“We simply cannot accept this aggressive policy, originally there was Crimea, then eastern Ukraine, now the Sea of Azov,” he said in the interview.

Mrs Merkel blamed Vladimir Putin, the Russian president, for the tensions, but warned that there is “no military solution” to the conflict in the region.