Question: Article:The OSCE monitors said in one case a vehicle marked "Cargo 200" - Russia's military code for soldiers killed in action - crossed from Russia into Ukraine on Tuesday and later returned.
Ukraine and the West accuse Russia of sending its soldiers to fight with separatist rebels in eastern Ukraine. The Kremlin denies the allegations.
More than 4,000 people have died in the conflict between Ukraine's military and pro-Russian rebels in the eastern Donetsk and Luhansk regions.
Nearly a million people have fled their homes since the fighting started in April, a month after Russia annexed Ukraine's southern Crimea peninsula.
The violence in the east has continued despite a ceasefire deal struck in Minsk, Belarus, in September, with both sides accusing each other of shelling and other violations of the agreement.
In its weekly report on Wednesday, monitors from the Organization for Security and Co-operation in Europe (OSCE) said the "Cargo 200" vehicle was seen crossing from Russia into Ukraine at the Donetsk border checkpoint, Rostov region, on 11 November.
They said it returned to Russia several hours later. The OSCE did not inspect the vehicle.
The border crossing on the Ukrainian side - Dovzhansky - is currently controlled by the separatist rebels.
In Kiev, Ukrainian security spokesman Andriy Lysenko said that five vehicles "belonging to the Rostov funeral service" had crossed the border on Tuesday.
He alleged that they had transported "Russian military men".
Ukraine has repeatedly stated that a number of Russia's regularly troops have been killed in fighting in the Donetsk and Luhansk regions.
Moscow denies the allegations as propaganda, but admits that what it describes as "Russian volunteers" are fighting alongside the rebels.
Meanwhile, the US envoy to the UN, Samantha Power, has accused Russia of undermining a ceasefire in Ukraine after reports of Russian troops and military hardware entering the country.
Speaking at a UN Security Council meeting on Ukraine on Wednesday, Ms Power said Russia was pursuing war in Ukraine while talking peace.
Russia's deputy ambassador to the UN, Alexander Pankin, dismissed the allegations.
The US called a meeting of the UN Security Council after Nato accused Russia of sending troops, artillery and air defence systems across the border into Ukraine.
Jens Toyber-Frandzen, the UN assistant secretary-general for political affairs, warned of "a return to full-scale fighting".
He said an alternative scenario - a simmering conflict "with sporadic low-level battles" - would also be "a catastrophe for Ukraine".
He also expressed concern at a third prospect - "a frozen or protracted conflict that would entrench the status quo in south-eastern Ukraine for years or decades to come".
Nato's top commander, US Gen Philip Breedlove, had earlier said that a Russian deployment in Ukraine - reported by Nato officials on Wednesday - might be intended to reinforce "pockets" under separatist control.
He did not specify how many troops, vehicles or weapons had been seen. A Nato official confirmed to the BBC that Nato had "assessed" that the equipment and troops were Russian in origin.
However, Russian defence official Maj Gen Igor Konashenkov said "there was and is no evidence" to support Gen Breedlove's claims.

A summary of the above article is?
Answer: Vehicles apparently used to transport soldiers' bodies have been seen crossing the Russian-Ukrainian border, monitors from Europe's security body have said.