The Ukrainian government accused Russia on Thursday of massing around 4,000 troops on the border of Russian-annexed Crimea and Ukraine, as multiple Crimean residents also reported seeing troop movements.

"According to our information, almost all military units of the Russian Federation stationed in the north of occupied Crimea... were pushed to the administrative border with Ukraine along with all their equipment and ammunition," said National Security and Defence Council spokesman Andriy Lysenko.

He said the units, totalling about 4,000 troops, were deployed in "small tactical groups" along the border in Crimea, the Ukrainian Black Sea peninsula that Russia annexed in March.

Ukraine's border service said Thursday that Russia was also using drones for air reconnaissance, with border guards reporting three cases of the use of drones in the last 24 hours, one near Mariupol in eastern Ukraine, and two on the Crimean border.

Crimea residents, who asked for their surnames not to be published, told AFP they had noticed recent Russian troop movements going towards the border.

"Tanks and some types of artillery were clearly seen moving on open railway cars through the station of Krasnoperekopsk towards Ukraine. I saw them myself," Sanie, a resident of the town of Krasnoperekopsk close to the border, told AFP.

She said that her friends in the village of Ishun, close to the highway that crosses the border, had also called her last week to say that "military hardware was going past all the time... about 20 at a time."

"There were several of these convoys. The vehicles were closed and they couldn't see what was inside: soldiers or equipment," Sanie said.

A resident of the town of Dzhankoy southeast of the border, Muzafer, confirmed he had spotted troop movements around a week ago.

"It's definitely the case that military vehicles were going towards the border then with soldiers," he told AFP.

An AFP reporter on Thursday saw three military vehicles carrying Grad multiple rocket launchers outside Crimea's main city of Simferopol.

A regional Tatar activist who asked not to be named said inhabitants of the village of Chongar, which straddles the border, reported seeing intensified Russian movements in the last few days including vehicles carrying Grad rocket systems and eight military transport helicopters.

The same activist said inhabitants of the village of Strelkovoye, which is on a spit formally on the Ukraine side, but where Russian paratroopers have been based since March, had also seen Russians move in more armoured vehicles and personnel in the last three to four days.

Russia's Defence Minister Sergei Shoigu said earlier this week that Moscow planned to boost troop numbers in Crimea because of what he described as a deteriorating situation in Ukraine and a buildup of foreign troops near its border.

Russia is deeply concerned at NATO's move eastwards and President Vladimir Putin has accused the West of provoking the crisis in Ukraine in order to "revive" the military bloc.

NATO this month agreed to boost its presence in eastern Europe, and the United States is currently staging war games in western Ukraine, along with another 14 countries.

Russia's Black Sea fleet is based in Crimea and Moscow announced in July that it had begun expanding and modernising it with new ships and submarines.

In weekend elections, Putin's ruling United Russia Party won more than 70 percent of the vote in Crimea's regional parliament, a poll the United States rejected as illegitimate.