NATO began wargames in Poland on Tuesday, with U.S. jets due to join the exercises as a gesture of Washington's support for its eastern allies after Russia's intervention in Ukraine, but bad weather delayed naval manoeuvres in the Black Sea.
Without naming neighbouring Ukraine, Polish President Bronislaw Komorowski called on his country's political parties to safeguard defence spending at a time of budget constraints due to the "events to the east".
The United States says both the air drills in Poland and its joint Black Sea exercises with Romania and Bulgaria were planned before the crisis in Ukraine. But they send a message of resolve to NATO members nervous about Russia's intentions in its former Cold War backyard, along with separate reconnaissance flights over Poland and Romania near the Ukrainian border.
At the Lask base in central Poland, Komorowski watched as four Polish F-16s took to the air. A U.S. Hercules transport plane landed with support staff and at least 12 U.S. F-16 fighter jets and 300 personnel are due to arrive by Thursday for the exercises, beefed up at Warsaw's request after Russian forces seized control in Crimea.
Flanked by a handful of U.S. soldiers, Komorowski stressed the need to maintain defence spending in Poland, a staunch U.S. ally still haunted by decades of Russian domination during the Cold War. "I hope events to the east of the Polish border, which is also NATO's border, will encourage tough decisions regarding Polish security," he told reporters.
Military funding in Poland, which marks the 15th anniversary of its accession to NATO on Wednesday, is under pressure.
Komorowski urged all parties to safeguard annual defence spending set by Polish law at 1.95 percent of gross domestic product (GDP). The parties are reluctant to cut back on welfare as an alternative before municipal and European Parliament elections this year and Polish parliamentary polls in 2015.
To the south, strong winds and high seas put back the Black Sea exercises by 24 hours, the Bulgarian defence ministry said. "The weather is now improving, the sea is not that rough and I don't expect another postponement," said Lieutenant-Colonel Dimitar Titev.
The USS Truxtun, a guided-missile destroyer with about 300 crew, had been due to join the drill in international waters southeast of the Romanian port of Constanta, some 350 km (220 miles) from Russian forces in Ukraine's Crimean peninsula.
The exercises underline Washington's lead role in the international response to Russia's actions in Ukraine, where political forces determined to take Kiev westwards to Europe have taken power after the overthrow of President Viktor Yanukovich.
The European Union, hampered by the need for consensus among its 28 members and their economic inter-dependence with Russia, has been less bold. 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 U.S. 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, U.S. Air Force General Philip Breedlove, a NATO spokesman said.
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 air 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.
"This was our request," said Siemoniak. "We really appreciate that the reaction was that quick and significant."
The USS Truxtun, part of the U.S. Sixth Fleet headquartered in Italy, is due to join the Bulgarian naval frigate Drazki and three Romanian vessels in the Black Sea drills.
It had been expected to visit the Bulgarian port of Varna March 12-14, but Titev said he was unable to confirm when it would arrive after bad weather closed the port on Monday. It was not expected the exercise would involve any live-firing.
(Additional reporting by Tsvetelia Tsolova in Sofia, Radu Marinas and Matthias Williams in Bucharest, David Mardiste in Tallinn; Writing by Matt Robinson; editing by David Stamp)