Istanbul/Kiev, April 25 : Turkish President Recep Tayyip Erdogan and his Ukrainian counterpart, Volodymyr Zelensky, discussed the latest developments of the Ukraine crisis over the phone. According to a statement by the Turkish presidential office on Sunday, Erdogan said the evacuation of the wounded and civilians from Ukraine's Mariupol, "where the situation is getting sad(der) each day," must be urgently ensured. Zelensky on Sunday tweeted that he stressed the need for the immediate evacuation of civilians from Mariupol, including Azovstal plant, and an immediate exchange of blocked troops. The two Presidents also addressed issues related to the negotiation process between Russia and Ukraine, Xinhua news agency reported. The Turkish President said Turkey has a positive stance on the guarantor issue in principle, and that his country is ready to provide all possible assistance for the negotiation process, the Turkish presidential office said. Following a fresh round of face-to-face talks between Russia and Ukraine in Istanbul in March, Ukrainian negotiators named several countries, including Turkey, which could act as guarantors. /IANS