Ukraine's President Petro Poroshenko has called elections being held in the rebel-held east of the country illegitimate.
He said that Ukraine and the rest of the world would reject the results, and called on Russia to do the same.
Ukrainian President Petro Poroshenko says Kiev has handed over 1,200 prisoners of war to the separatists as part of the ceasefire agreement.
Ukrainian President Petro Poroshenko has arrived in the south-eastern city of Mariupol, his press secretary Svyatoslav Tsegolko reported on Twitter.
President Poroshenko is quoted as saying: "We will not give up this land to anybody".
He also ordered the reinforced defence of Mariupol with tanks, rocket-launchers and aerial defence, according to Reuters.
Ukrainian President Petro Poroshenko has called for "effective international control" to guarantee a ceasefire agreed with separatists.
He said we must do "everything possible and impossible" to end the bloodshed in eastern Ukraine.
Ukraine's President Petro Poroshenko has confirmed that Kiev and separatist envoys have reached a ceasefire deal in Minsk.
He said he would order the Ukrainian military to cease fire from 6pm local time (4pm UK time) tonight.
Ukrainian President Petro Poroshenko has tweeted this photo showing him discussing the crisis in his country with other Nato leaders.
The seated figures are (L-R): French President Francois Hollande, President Poroshenko, US President Barack Obama, Prime Minister David Cameron and German Chancellor Angela Merkel. The sixth figure is believed to be Italian Prime Minister Matteo Renzi.
The Ukrainian government has confirmed that President Petro Poroshenko is on his way to the Nato summit in Wales.
He is expected to meet other Nato leaders today to discuss the crisis in the east of the country.
Russian President Vladimir Putin and his Ukrainian counterpart Petro Poroshenko have spoken by phone and "largely agree" on a possible way out of the Ukraine crisis, Interfax news agency reported, citing Putin's spokesman.
"The viewpoints of the presidents of the two countries largely coincide on possible ways out of the grave crisis situation," Dmitry Peskov was quoted as saying.
Ukraine's President Petro Poroshenko has said that he believes the crisis in the east of the country is very close to the point of "full-scale war".
He said that EU leaders agreed to prepare new sanctions against Russia, which could be implemented depending on the progress of his peace plan.
He added that he hopes a meeting with Russian amd EU representatives on Monday can bring about a ceasefire.
Ukraine president Petro Poroshenko has called on the European Union to give an "appropriate response" over Russian forces being brought into the country, his spokesman said on Twitter.