Nato is to deploy reconnaissance planes in Poland and Romania to monitor the Ukrainian crisis. The move comes as Russia appears to be cementing its control over the Ukrainian region of Crimea.
The Awacs (Airborne Warning and Control System) planes have some capacity to monitor vehicles on the ground but their chief mission will be reassurance. The flights will be mounted from bases in Germany and Britain, the BBC reports, and will all take place over Nato territory.
The United States has already sought to reassure its allies in Europe by adding six additional F-15 aircraft to the Nato air policing mission over the Baltic republics and is also despatching 12 F-16 fighters to a training exercise in Poland.
In Crimea on Monday, armed men - said to be Russian troops and local militias - have seized a military hospital where Ukrainian soldiers and veterans are being treated. They marched into the hospital in the regional capital, Simferopol, threatening staff and about 30 patients, some of whom are said to be seriously ill.
The hospital director says he was forced onto a bus and kept there for half an hour.
The attackers also herded staff into a reception to apparently meet "the new directors", Ukraine's Interfax-Ukraina news agency reports.
Separately, pro-Russian troops tried to capture a military transport base in Bahkchysarai, a town between Simferopol and Sevastopol. The gunmen fired warning shots into the air, but Ukrainian soldiers repelled the attack.
The BBC's correspondent in Crimea says that step by step, meeting very little resistance, pro-Russian troops are dismantling Ukraine's ability to resist in Crimea.