The United States has warned of a Russian provocation following reports of escalating fighting in eastern Ukraine.

"We have been saying for some time that the Russians could use such an approach to justify a military conflict," US Secretary of Defense Lloyd Austin said Thursday at the conclusion of a two-day NATO meeting in Brussels.

The reports of increasing shelling are therefore "disturbing", emphasized Austin.

Ukraine and the pro-Russian separatists in eastern Ukraine had previously accused each other of fueling the fighting in the conflict zone.

Meanwhile, the United States has received a response from Russia to the security guarantee proposals it submitted, according to a US State Department official.

The reply was delivered to the United States Ambassador to Russia, John Sullivan, in Moscow.

Russia is demanding security guarantees from the West and, among other things, the renunciation of Ukraine's admission to NATO.

The USA and the EU reject this.

Borrell: No one has any evidence of a deduction

Austin reiterated in Brussels on Thursday that the US has so far seen no signs of a Russian troop withdrawal.

On the contrary, Russia is even increasing the number of its 150,000 soldiers on the border with Ukraine.

In addition, Moscow is flying in additional military equipment and the operational readiness of the Russian forces in the Black Sea has been increased, the Pentagon chief emphasized.

London had also accused Russia of further increasing its troops.

EU foreign policy chief Josep Borrell also attended the NATO meeting.

He emphasized: "No one has any indication of a withdrawal of troops." Instead, there are signs of bombing in eastern Ukraine and an intensified Russian disinformation campaign.

When the time comes, the EU will not hesitate to "act decisively" and impose tough sanctions.

These mainly affect the energy sector, said Borrell.

Federal Defense Minister Christine Lambrecht (SPD) said on the sidelines of the meeting that she could not yet confirm any Russian troop withdrawal.

Russia has "enough troops and capabilities for a large-scale invasion of Ukraine with very little or no warning," NATO Secretary General Jens Stoltenberg said.

"That's what makes the situation so dangerous." He had previously confirmed that there was no credible evidence of a withdrawal by Russia from the border area with Ukraine.

He dismissed allegations from Belarus that the military alliance posed a potential threat to the country.

"NATO is not a threat, NATO is a defense alliance," he said after a defense ministers' meeting of the 30 member countries in Brussels. NATO, for its part, is "concerned" because Russia is modernizing its nuclear arsenal.

Belarusian head of state Alexandr Lukashenko had previously declared that he would be ready to station nuclear weapons in the event of a threat from the West.

Lukashenko spoke against the background of tensions between Western states and Russia as a Belarusian ally in the Ukraine crisis.

Minsk and Moscow started joint military exercises in Belarus last week, which are expected to last until February 20.

According to the Ministry of Defense in Moscow, units of the Southern Military District "completed their tactical exercises" in the Crimean peninsula and "returned to their home bases by train".

Television footage showed a train loaded with military vehicles crossing a bridge connecting Russia's annexed Ukrainian peninsula to the mainland.

The ministry also announced the return of armored units and other military vehicles to their bases.

According to US President Joe Biden and Chancellor Olaf Scholz, there is still a risk of Russian aggression against Ukraine.

During a phone call, both agreed that the situation in the region should be considered extremely serious in view of the massive Russian troop deployment in the border area with Ukraine, said the spokesman for the federal government, Steffen Hebestreit, on Wednesday.

A significant withdrawal of Russian troops has not been observed so far, the highest level of vigilance is required.

Both leaders welcomed statements by Russian President Vladimir Putin that diplomatic efforts should continue.

It is now important to pursue them further with high pressure.

It is important to enter into a constructive dialogue on questions of European security, to implement the Minsk agreements and to make progress in the Normandy format with the support of Germany and France.

The key to this lies in Moscow.

Russia surprisingly announced on Tuesday that after maneuvers the withdrawal of troops had begun.

At a meeting with Scholz in Moscow, Putin also declared that Russia did not want a new war in Europe.