MOSCOW -- The Ukrainian army on Friday claimed that soldiers came under artillery fire from the Russian side of the border overnight and were attacked by rebels in several other places in the restive east.
Ukrainian forces are trying to close in on the rebels, cutting them off from the border with Russia which Kiev believes is the source of arms and reinforcement. Moscow has vehemently denied a role in the conflict between pro-Russian separatists and government troops which has left more than 400 people dead and displaced tens of thousands.
In a statement on Friday, the headquarters of the government's military operation in the east listed at least seven locations where rebels attacked Ukrainian troops. They also claimed that attacks on two locations including a border crossing were supported by artillery fire from Russia.
The Obama administration on Thursday accused Russia of firing artillery from its territory into Ukraine to hit Ukrainian military sites and asserted that Moscow is boosting its supply of weaponry to pro-Russian separatists.
"We have new evidence that the Russians intend to deliver heavier and more powerful multiple rocket launchers to separatist forces in Ukraine and have evidence that Russia is firing artillery from within Russian to attack Ukrainian military positions," State Department spokeswoman Marie Harf told reporters. She said the evidence derived from "human intelligence information" but declined to elaborate, saying it would compromise sources and methods of intelligence collection.
The allegations come amid an increasingly bitter war of words between Washington and Moscow over the crisis in Ukraine and conflicting claims over the downing of a Malaysian passenger jet over eastern Ukraine last week. The U.S. has repeatedly accused Russia of stoking the Ukraine rebellion and has said it believes separatists shot down the Malaysian plane, killing nearly 300 people, with a Russian provided surface-to-air missile.
Harf said Wednesday the ultimate responsibility for the downing of the plane rests with Russian President Vladimir Putin and the Russian government.
Late on Thursday, Ukrainian troops entered the town of Lysychansk, which has been in rebel hands for several months, the military press office said. Rebels on Friday morning admitted in comments carried by Interfax that they had to flee the town which is 70 kilometers (45 miles) north-west of the regional capital Luhansk.
International observers from the Organization for Security and Co-operation in Europe on Friday were traveling to inspect the wreckage of the downed Malaysia Airlines plane and to search for more bodies. Human remains are still being found at the crash site more than a week after the plane went down.
All 298 people aboard Malaysia Airlines Flight 17 -- most of them Dutch citizens -- were killed when the plane was shot down on July 17. U.S. officials say the Boeing 777 was probably downed by a missile fired by pro-Russian rebels, likely by accident.