A US guided-missile destroyer carried out another round of navy drills in the Black Sea on Wednesday, the latest display of American military power just a few hundred miles away from Russian-annexed Crimea.

The USS Truxtun, a warship capable of carrying 96 missiles and torpedoes and equipped with a special radar system, performed exercises in calm waters with fellow NATO members Romania and Bulgaria, following a similar round last week.

US navy officials said last week's exercises were planned well before the current standoff between the West and Moscow over Russian troops occupying Crimea - the worst East-West crisis since the end of the Cold War.

But they have coincided with US and Polish fighter jets carrying out war games in Poland, and NATO reconnaissance flights over Eastern Europe, and send a message of reassurance to other NATO members nervous about Russia's intentions in its neighbourhood.

"There are many reasons for exercises with allies. It allows us an opportunity to assure our NATO allies that we support them," said Lieutenant Shawn Eklund, a spokesman for US naval forces in Europe, adding that the navy planned more.

"I cannot speak for the crew, but they train for the worst case. God forbid anything happens in this area. We are prepared, we work with our partners, with our NATO allies," he told Reuters.

He said the drills helped build effective cooperation between allies and demonstrated the US commitment to NATO.

"Hopefully that will serve to deter those who want to destabilise the region," Eklund said, adding that Wednesday's exercises were "recently planned" as a follow-up to those carried out last week.

Crimea voted in a Soviet-style referendum last weekend to leave Ukraine and join Russia, a vote that was condemned by the West and prompted Washington and Brussels to slap targeted sanctions on Russia, including asset freezes and travel bans.

In the latest chapter of the crisis, Russian troops backed by volunteers stormed Ukraine's naval headquarters in the Crimean port of Sevastopol on Wednesday, prompting a warning from Washington that Russia was on a "dark path" to isolation.

Drills aboard the Truxtun on Wednesday included Romanian Special Forces rappelling from a helicopter onto the ship, and communications exercises in which the allies shared information about their respective radar systems.

"It is a great opportunity to demonstrate our support... and also really interact with our allies," said 29-year-old Lieutenant Catherine Reppert, a tactical action officer, who sat in the combat control room next to a radar screen.

The naval exercises carried echoes of the response during another standoff between the West and Moscow in 2008, when Russian troops poured into Georgia to support the breakaway regions of South Ossetia and Abkhazia. At that time, NATO sent ships to the Black Sea on what it called pre-planned exercises, sparking Russian accusations of a naval build up.

The Truxtun was named after an American naval hero and featured last year in a Hollywood film.