US President Joe Biden said he would make it "very difficult" for Russia to carry out any invasion of Ukraine, after Kiev said it feared a large-scale military attack at the end of next January.

"I am in constant contact with our allies in Europe and with the Ukrainians," Biden said in remarks at the White House on Friday. "The Secretary of State and my National Security Adviser are widely involved in this matter."

"What I do is put in place a set of initiatives that I think will be the most comprehensive and meaningful to make it very difficult for (Russian President Vladimir) Putin to go ahead and do what people are afraid to do," he added.

In the same vein, White House spokeswoman Jen Psaki said, "We have a range of tools at our disposal. Of course, economic sanctions are an option."

Earlier, US Secretary of State Anthony Blinken said during a press conference on the sidelines of the OSCE meeting in Stockholm that any Russian attacks on Ukraine would result in economic sanctions that his country had not previously implemented.

Russian crowd

For his part, Ukrainian Defense Minister Oleksiy Reznikov said that intelligence reports indicate that Russia has amassed more than 94,000 soldiers near his country's borders, and may be preparing for a large-scale military attack at the end of next January.

Reznikov added, in a speech to the Verkhovna Rada, that his country will not take any provocative action, but is ready to respond if Russia launches an attack on it, stressing that Russia now has 41 military tactical battalions on standby in the Crimea.

He said that "the most likely time to launch an attack will be the end of January," stressing that Russia has begun "military exercises near Ukraine and is testing its communications."

But Moscow denies these allegations, and the Kremlin announced on Friday that Russia and the United States are working to organize a video meeting between Presidents Vladimir Putin and Joe Biden.

The Kremlin said that an initial date had been set for a video summit between the two presidents, but that Moscow was waiting for final approval from Washington.

Meanwhile, Al-Jazeera correspondent in Moscow reported that Russia is about to start military exercises near the border with Ukraine in 30 regions in the North Caucasus and the Rostov region bordering Ukraine, and in Crimea.

Moscow annexed Crimea from Ukraine in 2014, and has since been supporting separatists fighting the Ukrainian army in the east of the country.

This conflict has claimed more than 13,000 lives.