AFP, Berlin :German Chancellor Angela Merkel spoke Saturday to Russian President Vladimir Putin and Ukraine’s Petro Poroshenko in a bid to arrange a mini-summit that could actually end the ex-Soviet state’s separatist war.Merkel’s office said she stressed that Poroshenko’s attempt to convene a four-way leadership meeting in the Kazakh capital Astana on Thursday would succeed only if the warring sides committed themselves more to an existing truce.”The chancellor expressed concern about the continuing tensions and the humanitarian situation in the east of Ukraine,” German government spokesman Steffen Seibert said in a statement.Merkel added that talks in Astana that would also include French President Francois Hollande should only go ahead only if they made “concrete progress”.The four nations’ foreign ministers will meet in Berlin on Monday to make what Poroshenko hopes are final preparations for Astana.But Merkel signalled to Poroshenko on Saturday that she thought such a meeting may be premature.”A substantial coming together of positions on a ceasefire and the establishment of a demarcation line are needed,” said Seibert.