Updated at 1:00 p.m. ET.
Dutch experts charged with investigating the downing of a jetliner over eastern Ukraine have cancelled plans to reach the wreckage site amid fighting in the area between government forces and rebels.
NPR's Corey Flintoff reports from Donetsk, that as the fighting continues, "Ukrainian government troops appear to be gaining ground against the pro-Russian paramilitaries who control the wreckage site."
"Government troops are reported to be advancing on a key town north of Donetsk, and there is continued fighting on the edge of Donetsk itself," he says.
"The investigators, who are currently in Donetsk, have struggled to gain access to the rebel-controlled crash site, despite a truce between Ukrainian troops and separatist forces.
"'There is fighting going on. We can't take the risk,' said Alexander Hug, of the Organization for Security and Co-operation in Europe (OSCE).
"'The security situation on the way to the site and on the site itself is unacceptable for our unarmed observer mission,' he added."
The BBC says shelling was reported near the town of Grabove close to the MH17 crash and that rebels have prevented journalists from reaching the site. Ukrainian government forces are reportedly nearby.
Since Flight MH17 crashed on July 17, killing all 298 aboard, access to the debris field has been hampered by gun-battles between Ukrainian forces and rebels blamed for shooting down the plane with a surface-to-air missile.
The latest snag in reaching the plane follows an announcement by Malaysia's prime minister that an agreement had been reached with the rebels to let international police and investigators access the site.
Most of the passengers on the flight were Dutch and the Netherlands is leading the probe into the cause of the crash.
Meanwhile, the U.S. State Department on Sunday released satellite imagery it says proves Russian forces have fired rockets and artillery into eastern Ukraine in support of the rebels.
Moscow, which has been on the receiving end of U.S. and European ire for its backing of the Russian-speaking rebels, has reacted angrily to the latest round of EU sanctions, with the Kremlin saying the move will hamper cooperation and undermine the fight against terrorism and organized crime.
Reuters also quotes Russia's Foreign Ministry as accusing the U.S. "of contributing to the conflict in Ukraine through its support for the pro-Western government in Kiev."