Ten people have been killed in Donetsk, Ukraine after a shell hit a school in the rebel-held city, on the day students were set to return to class.  Terrified children were forced to shelter in the basement as the shelling yielded the highest daily civilian toll since a tenuous ceasefire was struck between Kiev and pro-Russian separatists last month.  Since then there have been clashes at several flashpoints around the region, with both sides blaming the other for violating the agreement that commits both to withdrawing weapons and establishing a buffer zone.  The United States has decried the violence while the European Union decided Tuesday to keep Russian sanctions in place, maintaining pressure on Moscow in what has become the worst East-West stand-off since the Cold War.  European Commission chief Jose Manuel Barroso also warned Russian President Vladimir Putin against introducing any new trade barriers against Kiev in a letter to the Russian leader.  The pro-Kiev regional government of Donetsk, which is now based in the government-controlled city of Mariupol, accused pro-Russian separatists of the "Donetsk People's Republic" of shelling the school.  "The Donetsk People's Republic used rocket launchers to shoot at a school ... the shell exploded five metres away from the building," the regional administration said in a statement.  Four adults were killed, it said.  Russian media and separatist websites showed footage of rebels launching attacks from positions in blocks of flats near Donetsk airport, which is still controlled by government troops. It lies about four kilometres from the school.  A source in Donetsk city hall told AFP that the strike happened right after the school's 70 pupils lined up for an assembly to mark the first day of class - held nationally on September 1 but pushed back by rebel authorities because of the conflict.  "The children were taken to the basement, they are still there," the source said.  Six more people died when another shell struck a public minibus in Donetsk, the regional authorities said.  The United States earlier decried the "intensifying violence" in eastern Ukraine and called on Russia and the rebels to hold fire.  "Since the ceasefire was signed ... attacks on Ukrainian positions and towns, including around the Donetsk airport ... have killed and wounded scores of Ukrainian armed forces and civilians," State Department spokeswoman Jen Psaki said.  "We call on Russia and the separatists it backs to immediately end these attacks."  She also called on Russia, which Kiev and the West blame for stirring the conflict, to withdraw all forces and equipment from the country.  Some Russian officers have however been working with Kiev since the weekend as part of a monitoring group.  With the toll climbing to 68 since the truce deal was struck on September 5, Ukraine today officially started its election season ahead of snap parliamentary polls on October 26.  Do you have any news photos or videos?
The EU has announced it is maintaining sanctions on Moscow, moments before NATO reported a continued presence of Russian soldiers in Ukraine.