New satellite images captured by a private U.S. company show that Russia has continued to build up its forces in annexed Crimea and near Ukraine in recent weeks while pressing the United States for talks over security guarantees it is seeking.

Reuters could not independently verify the latest images from U.S.-based Maxar Technologies. The Kremlin reiterated on Friday that it reserves the right to move its own forces on Russian territory as it sees fit and that Western countries were carrying out provocative military manoeuvres near its borders.

U.S., European and Ukrainian leaders have accused Russia of building up troops again near Ukraine's border since October after an earlier brief buildup in April, when Maxar also released images. U.S. President Joe Biden and other leaders say Moscow appears to be weighing an attack on Ukraine as soon as next month, something Moscow has repeatedly denied.

The images released late on Thursday showed a base in Crimea, which Russia annexed from Ukraine in 2014, packed with hundreds of armoured vehicles and tanks as of Dec. 13. A Maxar satellite image of the same base in October showed the base was half empty.

Maxar said a new brigade-level unit, comprised of several hundred armoured vehicles that include BMP-series infantry fighting vehicles, tanks, self-propelled artillery and air defence equipment, had arrived at the Russian garrison.

"Over the past month, our high-resolution satellite imagery has observed a number of new Russian deployments in Crimea as well as in several training areas in western Russia along the periphery of the Ukraine border," Maxar said in a statement.

It cited increased activity at three sites in Crimea and at five sites in western Russia.

President Vladimir Putin said on Thursday that Russia wanted to avoid conflict, but needed an "immediate" response from the United States and its allies to its demands for security guarantees. Moscow has said it expects talks with U.S. officials on the subject to start in January in Geneva.

When asked on Friday about the build-up of Russian troops near Ukraine, Kremlin spokesperson Dmitry Peskov said Moscow was acting to defend its own security.

"Russia is moving its own troops around on its own territory against the backdrop of highly unfriendly actions by our opponents in NATO, the United States and various European countries who are carrying out highly unambiguous manoeuvres near our borders," said Peskov.

"This forces us to take certain measures to guarantee our own security."

Biden has threatened strong economic and other measures if Russia invades Ukraine, building on sanctions imposed over Moscow's 2014 annexation of Crimea and backing for an ongoing separatist rebellion by pro-Russian forces in eastern Ukraine. A U.S. official has said new retaliatory measures could include tough export controls.

Russia says its wants NATO to halt its eastwards expansion and is seeking guarantees that the Western military alliance will not deploy certain offensive weapons to Ukraine and other neighbouring countries.

Other Maxar images showed a build-up at the Soloti staging ground in Russia close to the Ukrainian border, with photos shot at the start of December showing a larger concentration of military hardware than in September.

Other pictures showed continuing build-ups at Yelnya, a Russian town around 160 miles (260 km) north of the Ukrainian border, and at the Pogonovo training ground near the southern Russian city of Voronezh.