The leader of the party that narrowly won Greece’s election has begun urgent talks to form a coalition, saying he wants to forge a "national consensus”.Antonis Samaras, of the New Democracy party, on Monday met President Karolos Papoulias to be given a formal mandate.Mr Samaras said he would seek changes in the terms of a bailout agreement reached with the EU and IMF.The second-place Syriza party has rejected the terms of the bailout and said it would form the opposition.Mr Samaras said as he met the president: "A national understanding by everybody is imperative.”Under the constitution, Mr Papoulias has given Mr Samaras three days to form a government.Mr Samaras said he believed he could form a working coalition.Mr Papoulias said there was "a categorical imperative to form the government” immediately."The country cannot remain ungoverned for even an hour,” he said.‘Best guarantee’ Mr Samaras met the leader of Syriza, Alexis Tsipras, after talking to the president.Mr Tsipras said Syriza would remain in opposition and challenge the government, as his party had "different priorities”."The role of a strong and responsible opposition... is to intervene in a powerful way and this is what I assured Mr Samaras that we would do.”However, he said Syriza would not be an obstacle to the formation of a government by New Democracy, which he said was in accordance with the mandate of the people.Despite Mr Tsipras’s opposition, Mr Samaras said: "We need a national salvation government with as many parties as possible.”