Ukrainian armed forces have mounted a major onslaught against pro-Russian separatist fighters in an attempt to gain control over the area where a Malaysia Airlines plane was shot down earlier this month.
Russian state news agency RIA Novosti reported on Sunday that a column of Ukrainian armoured personnel carriers, trucks and tanks had entered the town of Shakhtarsk, 15km west of the site of the Boeing 777 crash.
Local media reported that fighting was also taking place in Snizhne and Torez, the two nearest towns to the crash site.
In a separate development, Ukraine's National Security Council said on Sunday that government troops had encircled Horlivka, a key rebel stronghold, and that there had been fighting in other cities in the east. Horlivka lies about 30km north of the main rebel-held city of Donetsk.
The armed forces "have increased assaults on territory held by pro-Russian mercenaries, destroyed checkpoints and positions and moved very close to Horlivka," the council said in a statement.
A representative of the separatist military command in Donetsk confirmed that there had been fighting in Horlivka, but said that rebel fighters were holding their positions.
Reports of the intensifying unrest in eastern Ukraine prompted a postponement of a trip to the site by a team of Dutch and Australian police officers who had planned to start searching for evidence and the remaining bodies.
Mark Rutte, the Dutch prime minister, said his government has rejected the idea of deploying armed troops to secure the crash site because there was no way they could achieve "military superiority'' in a region where heavily armed, pro-Russian rebels were battling Ukrainian government forces.
"The option we looked at was a military option in which you could secure the area so you can work in a stable environment,'' Rutte said.
But he added: "The option would be such a provocation to the separatists that it could destabilise the situation."
The US State Department has released satellite images that it says backs up its claims that rockets have been fired from Russia into eastern Ukraine and that heavy artillery for separatists has crossed the border.
A four-page document released by the State Department purports to show blast marks from where rockets were launched and craters where they landed.
Officials said the images, sourced from the US Director of National Intelligence, showed heavy weapons fired between July 21 and July 26 - after the July 17 shooting down of MH17.
Moscow has angrily denied allegations of any involvement in eastern Ukraine. Its foreign ministry over the weekend accused the US of conducting "an unrelenting campaign of slander against Russia, ever more relying on open lies".