Washington has been working on a package to boost surveillance and deploy more NATO vessels to the Black Sea after a naval confrontation between Moscow and Kiev last year, the US ambassador to NATO said.

The measure was expected to be discussed during talks by NATO foreign ministers in Washington on Wednesday and Thursday.

Russian President Vladimir Putin's spokesman Dmitry Peskov said the Kremlin viewed such a proposal "negatively".

"We do not understand what they mean by this. The situation with the Kerch Straight and navigation there is well known," he told reporters.

Russian deputy foreign minister Alexander Grushko told Russian news agencies the plan would only lead to "increased military risks" in the region.

"If additional military and technical measures are needed from our side, we will adopt them," Interfax news agency quoted Grushko as saying.

Most alliance members share concerns about Russia which backs separatists in a smouldering conflict in eastern Ukraine that has so far claimed some 13,000 lives.

In November, Russia fired on and seized three Ukrainian navy vessels, capturing two dozen sailors near the Kerch Strait, as they tried to pass from the Black Sea to the Azov Sea.

It was the first open military clash between Kiev and Moscow since 2014, when Russia annexed Crimea and a pro-Russian insurgency erupted in eastern Ukraine.

"We are going to make sure that we have the capability to deter a very aggressive Russia," US ambassador to NATO Kay Bailey Hutchison told reporters on Tuesday.

She said the US package was designed "to assure that there is a safe passage for Ukrainian vessels through the Kerch Strait."

Observers say that an increased NATO presence in the region is one of Russia's worst nightmares.

Putin has openly said that Moscow's decision to take over Crimea was partly motivated by NATO's expansion into Eastern Europe.

Peskov did not say Wednesday whether Russia would in fact allow NATO ships to pass through the Azov Sea.

"A decision will be made when there is such a request," the Kremlin spokesman said.

The West has accused Moscow of illegally blocking access to the Sea of Azov, used by both Russia and Ukraine.

A NATO spokesman declined to comment on the US ambassador's remarks but pointed to comments by Stoltenberg on Monday when he outlined plans to increase the alliance presence in the Black Sea.

Stoltenberg said NATO would step up port visits as well as exercises and training with Ukraine and Georgia.

But while he urged Russia to respect international law and the law of the sea, Stoltenberg made no mention of assuring freedom of navigation.