Dutch and Australian police have failed to reach the crash site of Malaysia Airlines flight MH17 for a second day as clashes rage in a town on the road to the area.

The international delegation of police and forensic experts were forced to stop in Shakhtarsk, a town around 20 miles (30km) from the fields where the aircraft came down.

Sounds of regular shelling could be heard from Shakhtarsk, with roads filled with cars carrying fleeing residents. Associated Press reported seeing a high-rise apartment block in the town being hit by at least two rounds of artillery.

The mandate of the police team is to secure the rebel-controlled area so that comprehensive investigations can begin and any remaining bodies be recovered.

Analysis of the black box flight recorders from the plane showed it was brought down by "massive explosive decompression" caused by shrapnel from a rocket blast, a Ukrainian official said on Monday. Andriy Lysenko told a news conference in Kiev that the information came from experts who have analysed the recorders.

Amid international recriminations over the chaos on the ground blocking access to the site, both sides in Ukraine's war blamed each other, with Kiev accusing the rebels of destroying evidence and the insurgents saying Ukraine's army was targeting civilians.

Authorities in Luhansk said on Monday that five people were killed and 15 injured in overnight artillery strikes. Three were killed in Donetsk as a result of clashes, the city's government said.

Washington released new photographs to bolster its claim that Russia – blamed by the west for stoking the insurgency by supplying arms including the missile that allegedly shot down MH17 – was taking a direct role in the conflict by firing into Ukraine.

Meanwhile, Russia demanded that the US "stop hindering" the work of monitors trying to check the situation on the ground.

The only point both sides appeared to agree on was the need for a ceasefire in eastern Ukraine, according to the Russian foreign ministry.

After days of preparing a joint armed force with Australia to secure the crash site, the Netherlands on Sunday dropped plans to deploy the officers over fears of being dragged into the conflict.

"Getting the military upper hand for an international mission in this area is … not realistic," said the Dutch prime minister, Mark Rutte. The country lost 193 citizens in the disaster.

"We concluded with our international partners that there's a real risk of such an international military mission becoming directly involved in the conflict in Ukraine," Rutte said.

An unarmed team of Dutch and Australian officers was forced to drop its plans to visit the site on Sunday as heavy bombardments rocked towns close to the site, where the remains of some of the victims still lie.

The Dutch foreign minister, Frans Timmermans, and his Australian counterpart, Julie Bishop, arrived in Kiev on Sunday to secure the agreement of the Ukrainian parliament over the police deployment.

So far, investigators have visited the site only sporadically because of security concerns, even though both Kiev forces and pro-Russian separatists had earlier called a truce in the immediate area around the site.

"Both sides have made assurances for the past 24 hours. There's been very intensive planning," said Michael Bociurkiw, spokesman for the Organisation for Security and Cooperation in Europe (OSCE) monitoring mission in Ukraine, before the team was due to set off for the crash site.

"We're aware that our time on the ground may be limited," he added.

Fighting continued overnight close to the crash site, with shelling heard in separatist bastion Donetsk, a city of 1 million people 40 miles (60km) away, which has been serving as a base for international monitors and journalists who are travelling regularly to the crash site.

An AFP reporter said bursts of gunfire also rang out in the centre of the city on Monday morning.

In Brussels, the EU is drafting tougher measures against Russia. Sanctions targeting economic sectors including an arms embargo are being considered. On Tuesday, the EU is expected to unveil more names of individuals and entities sanctioned.

Moscow has blasted the move as "irresponsible", and warned that it jeopardised cooperation on security issues.

About 1,000 people have been killed during the conflict, and the United Nations estimates that 230,000 have fled their homes.

The Red Cross said the country was in a state of civil war – a classification that would make parties in the conflict liable to prosecution for war crimes.