By Paul Carrel and Angeliki Koutantou BERLIN/ATHENS (Reuters) - German Chancellor Angela Merkel said on Thursday a deal between Greece and its creditors was still possible if Athens showed the necessary will, amid mounting pessimism that the austerity-hit country might crash out of the euro zone. Far from giving ground, Greek Prime Minister Alexis Tsipras launched a new attack on the lenders in an article in a German newspaper, slamming what he called their "blind insistence" on pension cuts he said would worsen his country's crisis. The leftist leader began a two-day visit to Russia to attend an economic forum in St. Petersburg as euro zone finance ministers gathered in Luxembourg to discuss the impasse.