Ukrainian armed forces mounted a major onslaught against pro-Russian separatist fighters Sunday in an attempt to gain control over the area where a Malaysia Airlines plane was downed earlier this month.
Reports of the intensifying unrest prompted a postponement of a trip to the site by a team of Dutch and Australian police officers that had planned to start searching for evidence and the remaining bodies.
Read: Rebels to let Malaysian police secure MH17 site
In Washington, the State Department released satellite images which it says show that Russia has fired rockets more than seven miles (11 kilometers) into eastern Ukraine.
The images, from the US Director of National Intelligence, show blast marks from where rockets were launched and craters where they landed. They are said to show strikes between July 21 and July 26.
Ukraine's National Security Council said that government troops have encircled Horlivka, a key rebel stronghold, and that there had been fighting in other cities in the east. Horlivka lies around 20 miles (30 kilometers) 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.
Elsewhere, Russian state news agency RIA Novosti reported Sunday that a column of Ukrainian armored personnel carriers, trucks and tanks had entered the town of Shakhtarsk, 10 miles (15 kilometers) west of the site of the Boeing 777 crash.
Shakhtarsk is a strategic town in the area. By controlling the town, the Ukrainian army would cut off vital rebel supply lines.
Local media reported fighting also taking place in the towns of Snizhne and Torez, the two nearest mid-sized towns to the crash site.
The government accused rebel forces of firing rockets Sunday on residential apartment blocks in Horlivka in what they said was an attempt to discredit the army and whip up anti-government sentiment. The separatist self-declared "Donetsk People's Republic" has accused the army of being responsible for that and other rocket attacks in nearby cities.
The Donetsk regional government - which is loyal to Kiev and based elsewhere since rebels took over the area - said Sunday in a statement that at least 13 people, including two children aged 1 and 5, were killed in fighting in Horlivka. It said another five people were killed as a result of clashes in a suburb north of Donetsk.
New York-based Human Rights Watch last week condemned what it said was the Ukrainian government forces' practice of using unguided rockets in populated urban areas. It said that use of the rockets was a violation of international humanitarian law that "may amount to war crimes."
Malaysian Airlines Flight 17 was shot down with a surface-to-air missile over a part of eastern Ukraine controlled by pro-Russian separatists on July 17, killing all 298 people on board. US and Ukrainian officials say it was shot down by a missile from rebel territory, most likely by mistake.
Ten days after the disaster, a full-fledged investigation still has not begun at the crash site, with some bodies still unrecovered and the site forensically compromised. Concerns about the integrity of the site were raised further when a couple that had flown from their home in Perth, Australia, visited the site Saturday outside the village of Hrabove and even sat on part of plane's wreckage.
It remained unclear when the forensic experts from the Netherlands and Australia would be able to begin their work at the site.
Alexander Hug, the deputy head of a monitoring team from the Organization for Security and Cooperation in Europe, said it was too dangerous for the unarmed officers to travel there from their current location in Donetsk.
"We reassess the situation continuously and we will start to redeploy tomorrow morning back to the site if the situation changes," Hug said.
Australian prime minister Tony Abbott had said earlier Sunday that unarmed Australian police would be part of the Dutch-led police force to secure the area and help recover victims' remains.
Abbott said that by using unarmed police, Ukraine's Parliament will not need to ratify the deployment as it would if the security force were to be armed.
"This is a risky mission. There's no doubt about that," Abbott told reporters. "But all the professional advice that I have is that the safest way to conduct it is unarmed, as part of a police-led humanitarian mission," he said.
Malaysian Prime Minister Najib Razak said in a statement that his country would send dozens of police and that his country had received assurances from pro-Russia separatists that they would provide protection for investigators.
Flights from Ukraine to the Netherlands have taken 227 coffins containing victims of the plane disaster. Officials say the exact number of people held in the coffins still needs to be determined by forensic experts in the Netherlands.
The Malaysia Airlines disaster prompted some expectations in the West that Russia would scale back its involvement in the uprising in Ukraine's east, but the opposite seems to be the case.
In addition to producing evidence that rockets have been fired into Ukraine from Russia, the United States has said it has seen powerful rocket systems moving closer to the border.
In Warsaw, about 250 people marched through the city to protest what they called the "terror" imposed by Russian President Vladimir Putin in Ukraine. Some of the demonstrators carried Ukrainian flags, and there were banners that proclaimed "Putin is a Sponsor of Terror" and "Europe, Stop Just Talking. Start Taking Action! Stop Terror in Ukraine."