WARSAW - The United States will signal its resolve to protect its NATO allies near Russia's borders on Tuesday with the start of the first joint military training exercises in the region since the Kremlin intervened in Ukraine.
In the Black Sea, across the water from the Crimean Peninsula where Russian military groups have seized control from Ukrainian authorities, a US navy destroyer will take part in manoeuvres with Romanian and Bulgarian warships.
To the north in Poland, US fighter jets are arriving at the central Lask air base to take part in joint exercises, with Poland's president expected to review the manoeuvres.
The United States stressed that both training drills were planned before the Ukraine crisis, but they are also a signal of support for NATO members nervous that if Russia is prepared to intervene in Ukraine, they could be next.
The exercises underline that it is Washington which has so far taken the lead in the international response to Russia's actions in Ukraine, while the European Union, hampered by the need for consensus among its members, has been less bold.
In Poland - a staunch US ally still haunted by decades of Russian domination during the Cold War - officials say the scope of the air exercise was beefed up specifically in response to the Russian intervention in Crimea.
Speaking on Monday at a Polish rocket defence site, not far from the Russian Baltic Fleet's base at Kaliningrad, Polish defence minister Tomasz Siemoniak said the exercise was to have been smaller, involving only transport aircraft.
But Siemoniak said that after the Russian military intervention in Crimea, Warsaw asked the Pentagon to send fighter jets instead. At least 12 F-16 fighters would be arriving in Poland this week, with 300 service personnel.
"This was our request," said Siemoniak. "We really appreciate that the reaction was that quick and significant." Polish President Bronislaw Komorowski is scheduled on Tuesday to visit Lask, which is expected to be the focus of the exercises.
The Kremlin has said it acted to protect Russian citizens in Crimea from attack, and denies invading the region.
In a separate deployment since the Ukraine crisis began, extra US military aircraft have arrived in Lithuania to take part in regular NATO air patrols over the Baltic states.
The alliance also said on Monday that it would start reconnaissance flights over Poland and Romania to monitor the situation in neighbouring Ukraine. NATO ambassadors gave the go-ahead to the AWACS flights, acting on a recommendation by the alliance's top military commander, US Air Force General Philip Breedlove, a NATO spokesman said.
The US warship taking part in the Black Sea manoeuvres is the USS Truxtun, a guided-missile destroyer with about 300 crew which is part of the US Sixth Fleet headquartered in Italy.
Joining it in the exercises will be the Bulgarian naval frigate Drazki, and three Romanian naval vessels, Bulgaria's defence ministry said in a statement. The drill would take place in international waters southeast of the Romanian port of Constanta, it added.
Constanta lies about 350 km (220 miles) from the Crimean port of Sevastopol, where Russia's Black Sea fleet leases a base. "The goal of the exercise is to increase the operational compatibility within NATO members' navy vessels, to improve the mutual understanding and to increase the crews' preparedness at sea," the ministry said.
It was not expected the exercise would involve any live-firing. The US military said last week the presence of the USS Truxtun had been planned weeks in advance, and that the exercises were routine