Kiev: International observers issued a stark warning over escalating violence in eastern Ukraine on Tuesday as Dutch investigators hoping to recover debris from a doomed airliner left the MH17 crash site empty-handed.
The Organization for Security and Cooperation in Europe (OSCE) said there was a "rising" risk that unrest in the war-torn region would get worse amid fears of a return to all-out fighting.
A fragile ceasefire has been in place in the east of the former Soviet republic since September but has been regularly shaken by localised outbreaks of fighting.
"The level of violence in eastern Ukraine and the risk of further escalation remain high and are rising," Michael Bociurkiw of the OSCE`s Special Monitoring Mission to Ukraine told a press conference in Kiev.
"More than two months after the signing of the Minsk protocol memorandum, the firing has not ceased," he said.
Earlier Tuesday, OSCE observers reported seeing a convoy of 43 unmarked military trucks -- five towing Howitzer heavy artillery pieces and another five multi-launch rocket systems -- travelling into the rebel stronghold of Donetsk.
It was the latest in a string of reports of unmarked trucks and heavy weapons in rebel-controlled areas in the city in recent days.
In a further indication of escalating violence, Ukraine`s military reported that five of its soldiers had been killed and nine injured in the east over the past 24 hours.
The conflict in Ukraine -- which has killed some 4,000 people since April, according to UN figures -- has plunged relations between Russia and the West to their lowest since the Cold War.
Several big cities in eastern Ukraine are controlled by pro-Russian separatists.
While Western powers have repeatedly voiced concern at Ukrainian claims that Russia is supporting them, Moscow denies any involvement.Meanwhile, Dutch investigators hoping to start removing the wreckage of Malaysia Airlines flight MH17, which crashed in July killing 298 people, are trying to negotiate access to the site with rebels.
A team of around a dozen experts arrived in a convoy of cars earlier Tuesday but were not permitted to enter the crash zone and later left.
"We hope that the removal of debris can start as soon as possible but that depends on the situation on the ground," Wim van der Wegen, a spokesman for the Dutch Safety Board, told AFP.
Rebels cited by Russian news agencies said the team had abandoned efforts to collect debris Tuesday as negotiations stumbled over a protocol for the project.
Ukraine, supported by Western nations, accuses Russia of supplying the pro-Kremlin separatists with the missile that shot down the plane, while Moscow and the rebels have pointed the finger of blame at Kiev`s forces.
Russian President Vladimir Putin is facing renewed Western diplomatic pressure over the issue during a week of high-level international talks.
Putin discussed Ukraine with US President Barack Obama and Australian Prime Minister Tony Abbott at the Asia Pacific Economic Cooperation (APEC) summit in Beijing.
Earlier Tuesday, US deputy national security adviser Ben Rhodes told reporters: "We continue to be deeply troubled by Russian activities. If they continue... it`s a recipe for isolation."
Meanwhile, Abbott pointed out to Putin that the United States, after it downed an Iranian passenger jet over the Gulf in 1988, had expressed its regrets "and made appropriate restitution".
"He commended the precedent to President Putin," a statement from Abbott`s office said.
The Australian leader had previously threatened to "shirtfront" (confront) Putin over MH17, which was carrying 38 citizens or residents of Australia, but "did not try" to follow through on the threat, a Kremlin spokesman said.
Australia will host this week`s G20 summit in Brisbane where more such talks are likely.
The United States and European Union have shown their anger towards Russia over Ukraine with a string of sanctions designed to weaken its economy. The ruble has lost some 25 percent of its value this year.
EU foreign ministers are set to hold a meeting on Ukraine next Monday and will discuss the option of more sanctions, EU foreign policy chief Federica Mogherini said in Berlin on Tuesday.
But German Chancellor Angela Merkel said that, while EU member states were considering adding pro-Russian separatists to existing sanction lists imposed on Moscow, no more economic sanctions were planned "at the moment".