DONETSK, Ukraine — Ukrainian government officials said their forces advanced to the outskirts of a key town north of Donetsk on Saturday and are battling to retake the stronghold held for months by pro-Russia rebels.
The operation comes as Ukrainian forces have gained some momentum by retaking control of territory from the rebels. But Russia appears to have become more involved in the fighting, with the United States and Ukraine accusing Moscow of moving heavy artillery across the border to the rebels.
Ukrainian national security spokesman Andriy Lysenko said Ukrainian forces were outside Horlivka, just north of the regional center of Donetsk.
If they can take Horlivka, it would open a route to Donetsk, Lysenko said. ‘‘The approaches to Donetsk are being blocked so that the terrorists do not get the chance to receive ammunition, reinforcements or equipment,’’ he said, referring to the rebels.
Donetsk, a city of about 1 million people, is a major center of the separatist uprising that has battled Ukrainian government forces for five months.
The highway north of Donetsk was blocked by rebels. Explosions were heard from the direction of the town’s airport, on the northwest edge of the city, an area frequently contested by Ukrainian forces and rebels. Black smoke was seen in the direction of Yakovlikva, a northern suburb of Donetsk.
About 35 miles to the east, the site where Malaysia Airlines Flight 17 was shot down was still eerily empty except for the parents of one of the 298 people killed in the July 17 disaster. A full-fledged investigation still has not begun because of the security risks posed by the nearby fighting.
The team of investigators from the Netherlands has not been able to travel to the site because of security concerns.
But Jerzy Dyczynski and Angela Rudhart-Dyczynski, parents of 25-year-old Fatima, traveled from their home in Perth, Australia, to honor their daughter. They crossed territory held by pro-Russia rebels to reach the wreckage-strewn fields outside the village of Hrabove, where they sat together on part of the debris, his arm around her shoulder.
Fatima ‘‘was for peace. She will be forever for peace,’’ her father said.
US and Ukrainian officials say the plane was shot down by a missile from rebel territory, probably by mistake.
Two military cargo planes, one Dutch and the other Australian, flew 38 more coffins carrying victims to the Netherlands for identification and investigation. Later, the Dutch government said the first formal identification of a victim had taken place. The name and sex of the victim, a Dutch national, were not released.
The military cargo planes took off Saturday from Kharkiv, a government-controlled city where the bodies have been brought from the wreckage site. They landed later in the afternoon in Eindhoven, where the coffins were transferred to a fleet of hearses in a solemn ceremony.
Officials said the flights took the last of the 227 coffins containing victims that had been brought to Kharkiv by refrigerated train. Officials say the exact number of people held in the coffins is still to be determined by forensic experts in the Netherlands, where Ukraine agreed to send the bodies.
International observers have said there are still remains at the wreckage site.
The disaster sparked hopes in the West that Russia would scale back its involvement in the uprising in Ukraine’s east, but nine days later the opposite seems to be the case.
Russia launched artillery attacks from its soil into Ukraine on Friday, according to Ukrainian military officials, while the United States said it has seen powerful rocket systems moving closer to the Ukraine border.
Those accusations sparked a strong denial from Moscow, which accuses the United States of a smear campaign.
The Russian Foreign Ministry on Saturday said the United States was conducting ‘‘an unrelenting campaign of slander against Russia, ever more relying on open lies.’’
The ministry took particular issue with comments Friday by White House spokesman Josh Earnest, who said Washington regards Moscow as involved in the shooting down of the airliner because it allegedly has supplied missile systems to the rebels and trained them on how to use them.
The ministry complained that these allegations have not been backed up with public evidence and it sneered at Earnest for saying they are supported by claims on social media.
‘‘In other words, the Washington regime is basing its contentions on anti-Russian speculation gathered from the Internet that does not correspond to reality,’’ it said.
Russia also lashed out at the latest round of Ukraine-related sanctions imposed by the European Union, saying they endanger the fight against international terrorism.
The EU sanctions, revealed Friday, impose travel bans and asset freezes on 15 people, including the head of Russia’s Federal Security Service and the head of the agency’s department overseeing international operations and intelligence.