MOSCOW: A Russian border security official said Monday that more than 400 Ukrainian soldiers have crossed into Russia, although both sides gave conflicting accounts as to why they had decided to cross the border.

The Russian official said the soldiers deserted the Kiev government and the Russian side opened a safe corridor. A Ukrainian military official, who did not give a number for the soldiers involved, were forced into Russian territory by rebel fire after running out of ammunition.

The Interfax news agency reported that Russia’s air force began military drills in central and western regions of the country, a move that could spark further fears that Moscow is ready to flex its military muscle in Ukraine.

The drills will start Monday and last through Friday, air force chief Igor Klimov was reported as saying, and will involve more than 100 fighter jets and helicopters.

Vasily Malayev, head of the Federal Security Service’s border patrol in the Rostov region, said that 438 Ukrainian soldiers had reached Russian territory on Monday. He said the Russian side had allowed the soldiers to safely enter the country overnight.

The ITAR-Tass news agency quoted Malayev as saying that 180 of the soldiers had requested to be sent back to Ukraine, and that the Russian side would help travel back.

Russia’s Defense Ministry couldn’t immediately be reached for comment.

The Ukrainian military confirmed that part of a brigade had most likely crossed into Russian territory, although it disputed Russia’s version of events and wouldn’t say how many soldiers went over.

The Ukrainian army is deploying tactical missile launchers and multiple rocket-launch systems near Donetsk in east Ukraine, the Russian Foreign ministry said on Monday.

“The Ukrainian army keeps concentrating Tochka U rocket systems, as well as Smerch (Tornado) and Uragan (Hurricane multiple-launch rocket systems), near Donetsk,” it said in a written statement. “How many more lives will these weapons take?” On Monday, Malaysian experts joined Dutch and Australian police for the first time as they continued combing the area for traces of the victims, according to a statement from the Dutch security and justice ministry.

The experts were briefly prevented from accessing the rebel-held site but eventually let through, according to the Organization for Security and Cooperation in Europe (OSCE), which has been monitoring the situation in Ukraine and has monitors accompanying the experts.

“Work has resumed at the MH17 crash site by 100-plus experts,” it tweeted Monday afternoon. Sniffer dogs were accompanying the experts, it had said.

In all, 124 experts were present at the scene and “planned to explore two fields west of the crash site,” the government in Kiev said in separate statement.

In a statement posted on his Facebook page, Malaysian Transport Minister Liow Tiong Lai vowed that arrangements to repatriate the bodies of its citizens killed in the crash would be made “once bodies have been identified and the necessary forensic work completed.”

“Efforts to locate and identify victims of the MH17 tragedy continue,” he added, noting that a national day of mourning would be organized once all remains of the Malaysian victims have returned home.

Ukrainian government forces recaptured an important railway hub from pro-Russian rebels in the east of the country, with five soldiers killed and 15 others wounded over the last 24 hours, a security official in Kiev said on Monday.

A rebels’ Facebook page dismissed government forces taking Yasynuvata as a lie.

Kiev has intensified its campaign against the Moscow-backed separatists and made steady gains since a Malaysian airliner was downed over rebel-held territory on July 17.

Government troops have now all but encircled the rebels’ second-largest stronghold of Luhansk and rebels have declared a “state of siege” in Donetsk, the largest city they hold. Luhansk has been left without electricity or running water and the mobile network is also down, local officials said on Monday.

“Units taking part in the anti-terrorist operation yesterday took the town of Yasynuvata, which is an important hub of the region’s railway system,” Andriy Lysenko, a spokesman for Kiev’s military operation in the east, told a media briefing.

Separatists seized Yasynuvata — just north of Donetsk nearby a main road leading to Luhansk — in May.

Lysenko also said a group of Ukrainian soldiers and border guards, who have been stuck between the Russian border to the east and pro-Russian rebel position in the west for more than three weeks, crossed into Russia in the early hours of Monday.

“Today at 4:30 a planned operation took place to unblock a Ukrainian military unit nearby Chervonopartyzansk. A large part (of the unit) successfully ... reached a safe place,” he said.

“Part of the soldiers (group) went into the Russian territory,” he said, noting that Kiev was now trying to negotiate their return. He refused to say how many servicemen had crossed the border but the wife of one of them, speaking on Ukraine’s 112 TV channel, put the number at about 200.

On the Malaysian Boeing crash site, international experts started recovery and investigative work on Monday.

“After a delay due to fighting, the team of Australians, Dutch and Malaysian experts began work,” a statement by the Dutch mission said.