Donetsk, Ukraine (CNN) -- Long lines of cars jammed the roads leading south out of Donetsk in eastern Ukraine Saturday, as residents attempted to flee the city center after a night of heavy shelling on the city's northern outskirts.
Hundreds of vehicles were caught in heavy traffic, and trains are no longer running in and out of the city, which is a stronghold for the pro-Russia rebels.
There was heavy shelling and antiaircraft fire on the outskirts of the city to the north throughout the night. There has been sustained fighting in the area for weeks, but it appeared more intense overnight than in recent days.
Russian news agency Interfax reported a dramatic increase in the number of Ukrainian refugees seeking refuge over the border in Russia.
"The Ukrainian government officials were seeking to encircle the city, really squeeze the remaining pro-Russian separatist forces that had fallen back there since being driven out of other strongholds across Eastern Ukraine," said CNN's Phil Black, reporting from a congested road in Donetsk while scores of people attempted to leave.
"It appears the Ukrainian government forces moving closer to the city, perhaps with the intention of retaking it," said Black. "At the southern outskirts of the city again, we saw a very big presence of Ukrainian armored vehicles; tanks, artillery, armored personnel carriers."
An additional 4,600 people have moved into temporary camps over the past 24 hours, Interfax cited Russian Emergency Situations Ministry spokesman Alexander Drobyshevsky as saying. This has pushed the total number of refugees staying in such camps above 31,000, he said.
Russia has opened 20 new temporary settlements for Ukrainian refugees in the past day, Drobyshevsky told Interfax, bringing the total number provided to 433. More than 11,000 children are among those staying there, he said.
CNN cannot independently confirm the report.
According to the latest figures from the United Nations' refugee agency, UNHCR, a total of 141,972 Ukrainians have fled to Russia this year because of unrest in eastern Ukraine, based on information from the Russian Federal Migration Service as of July 22. More than 41,000 of those Ukrainians are reported to have applied for asylum.
An additional 101,617 Ukrainians were reported as internally displaced within Ukraine as of July 22, the UNHCR said.
However, the refugee agency noted that because of the lack of a centralized registration system, the real number of those who have fled their homes is unknown and is likely to be higher.
"Various organizations report that some displaced persons from the East are reluctant to apply to the authorities because they fear retribution, want to maintain a low profile, and moreover, see little benefit in identifying themselves as there is no special reception procedures established for them," the UNHCR said.
CNN freelancer released by pro-Russian rebels
A Ukrainian journalist detained Tuesday by pro-Russian rebels while working as a freelance producer for CNN has been freed.
Anton Skiba called CNN on Saturday to confirm his release. CNN also received visual confirmation that Skiba is free from sources on the ground in Donetsk.
On Tuesday evening, armed fighters led by a senior official from the self-declared Donetsk People's Republic were waiting outside the Donbass Palace Hotel, in the rebel-controlled city of Donetsk, as a CNN television crew returned from a day's work at the crash site of Malaysia Airlines Flight 17.
Skiba had worked for one day with the CNN crew when he was detained.
An official with the Donetsk People's Republic initially accused Skiba of "terrorism" and of posting offers, on his Facebook page, of cash rewards for the killing of rebel fighters.
The official later dropped the accusation about the Facebook posts and said Skiba was being questioned for having multiple forms of identification with different surnames.
Investigation into crash hampered
More than a week after Malaysia Airlines Flight 17 came down in eastern Ukraine, Malaysian investigators have not yet been able to access the entire crash site, Malaysian Prime Minister Najib Razak said Saturday.
He urged both the pro-Russia rebels and Ukraine's armed forces to cooperate so investigators can access the site fully.
All 298 people aboard the plane died when it crashed on July 17. Of that number, 43 were Malaysian, including 15 crew and two infants, according to Malaysia Airlines.
Nine days later, some human remains still lie scattered amid the debris.
The rebels controlling the area -- the same rebels that Ukraine and the United States accuse of downing the plane -- hinted on Friday to an international monitoring group that they've nearly had enough of the crash investigation, even with the limited number of investigators they've let in so far.
"We were given the indication ... that their patience is almost wearing out," said Michael Bociurkiw, a spokesman for the Organization for Security and Co-operation in Europe, which has had a small team touring the site for days. "They're saying maybe another week and then they don't know what would happen."
More coffins flown out of Ukraine
Another 38 coffins arrived on two planes from the Ukrainian city of Kharkiv and were given a somber welcome in the Dutch city of Eindhoven on Saturday. This is expected to be the last transfer of coffins from Ukraine to Netherlands for the time being. The search for further remains at the crash site will continue when possible.
Meantime, authorities for the first time released the identity of a victim of Dutch nationality. A team of more than 200 specialists are busy with the identification process, but officials have stressed the process could take months.
A group of Dutch forensic experts was unable to reach the crash site Saturday because of safety concerns prompted by renewed fighting in the Donetsk area, a spokesman for the Dutch Ministry of Defense said. He said it was also too dangerous for OSCE observers to return to the site.
The site is still not secured by the Ukrianian government or any international force.
Of the 298 people on board the downed airliner, 193 were Dutch citizens.
CNN's Ingrid Formanek and Phil Black reported from Donetsk and Laura Smith-Spark wrote and reported in London. Journalist Victoria Butenko contributed to this report.