Four civilians were killed and nine wounded by shrapnel during fighting on Saturday and Sunday in eastern Ukraine's separatist stronghold city of Donetsk, local officials said.Pro-Russian rebels and government forces have continued to clash on the city's outskirts despite a Sept. 5 ceasefire accord that has generally contained violence in other parts of the country's contested east..Speaking at a daily security briefing in Kiev on Sunday, military spokesman Andriy Lysenko said 13 Ukrainian servicemen had been wounded in the past 24 hours in fighting in the east. There was no immediate word on casualties among rebel fighters.The sounds of mortar fire and rocket launchers thundered through central Donetsk throughout Saturday night as fighting went on several kilometers (miles) away.Residential areas of Donetsk are often caught in crossfire as they right sit next to the city airport, a strategic and symbolic target that neither side has been able to take full control of during a prolonged stand-off.Fighting around the airport picked up towards the end of the week as world leaders - including Russian President Vladimir Putin and Ukrainian President Petro Poroshenko - discussed the crisis during talks in Italy. They made little progress on ways to stop the violence.Kiev and the West accuse Russia of fanning the armed conflict in eastern Ukraine. They have imposed sanctions on Moscow, who they see as guilty of providing support, including arms and troop reinforcements, to the rebellion.Moscow shares the separatists' dislike of Kiev's pro-Western government, but denies playing a role in the armed conflict. However, low-ranking separatist fighters on the ground sometimes admit the presence of Russian troops in eastern Ukraine.