"The Ukrainians have taken over a part of the crash site," said Vladimir Antyufeev, self-styled first deputy prime minister of the "Donetsk People's Republic".
Ukraine's military said its troops are battling separatist fighters for control of a string of towns around the impact site and had "entered" the town of Shakhtarsk, some 10 kilometres from the scene.
The rebels, accused by Ukraine and its Western allies of shooting down MH17 on July 17, have kept a close guard over the crash site as international anger has grown over possible evidence tampering.
A team of unarmed Dutch and Australian police were forced by heavy fighting to abandon attempts to reach the crash site, where the remains of some of the 298 people killed in the disaster remain rotting in the sun.
But Antyufeev lashed out at Kiev for launching the attack on the site despite the planned visit by international experts and said government shelling was "destroying parts of the site where fragments of the plane are located".
Today's advances by Kiev forces around the crash site come as the government claims a string of government victories across the wider region that could see the main rebel stronghold of Donetsk cut off from the Russian border.
Antyufeev admitted that the rebel forces increasingly have their backs to the wall and that the military situation on the ground "is very complicated, it is not a secret".