Ukraine accused Russia of staging an "armed invasion" of Crimea as the ex-Soviet state's ousted leader prepared to emerge defiant from five days of hiding after winning protection from Moscow.
Unidentified armed men were patrolling outside of Crimea's main airport early Friday while gunmen were also reported to have seized another airfield on the southwest of the peninsula where ethnic Russians are a majority and where pro-Moscow sentiment runs high.
Western governments have been watching with increasing worry as Kiev's new pro-EU rulers grapple with dual threats of economic collapse and cession from Russified southern and eastern regions of the divided nation, which had backed fugitive ex-president Viktor Yanukovych.
Russian President Vladimir Putin this week stoked concerns that Moscow might use its military might to sway the outcome of Ukraine's three-month standoff by ordering snap combat drills near its border involving 150,000 troops and nearly 900 tanks.
Ukraine's interim president Oleksandr Turchynov responded on Thursday by declaring that any movement of Russian troops out of their Black Sea bases in Crimea "will be considered as military aggression".
US Secretary of State John Kerry attempted to relieve diplomatic pressure that has increasingly assumed Cold War overtones by announcing that Russian Foreign Minister Sergei Lavrov had assured him that Moscow "will respect the territorial integrity of Ukraine."
Putin also appeared to take a more conciliatory approach late on Thursday by vowing to work on improving trade ties with Ukraine and promising to support international efforts to provide Kiev with funds that could keep it from declaring a debt default as early as next week.
Yet tensions continued to soar by the hour in the Russian-speaking Crimea - a scenic Black Sea peninsula that has housed Kremlin navies for nearly 250 years and was handed to Ukraine as a symbolic gift by a Soviet leader in 1954.
Ukraine's Interior Minister Arsen Avakov accused the Russian armed forces of being directly involved in armed dawn raids on an airport in Crimea's main city of Simferopol as well as an airfield on the southwestern coast.
Dozens of men armed with Kalashnikovs encircled the Simferopol airport on Friday morning after reports suggested that they had briefly seized control of its runway.
An administrator said the "airport was operating normally" on Friday morning despite the presence of the armed men in battle fatigues.
Several supporters of the apparently pro-Russian gunmen said the armed men arrived after reports that members of the country's new pro-EU government were planning to fly to Simferopol.
Unconfirmed reports by Ukrainian media said armed men had also seized the Belbek airfield near the city of Sevastopol, which is home to Russia's Black Sea fleet.
Avakov accused the Russian armed forces of being behind both incidents.
He said gunmen at the Simferopol airport "are not even hiding the fact that they belong to the armed forces of the Russian Federation."
The interior minister added that the Belbek airfield was "blockaded by military units of the Russian navy."
"I consider what is happening to be an armed invasion and an occupation," Avakov said in a statement posted on his Facebook account.
But Russia's Interfax news agency quoted an unnamed source as saying that the Belbek air field was under the control of local pro-Russian self-defence units who had no links to the Black Sea fleet.
The peninsula of nearly two million people has been in crisis since dozens of pro-Kremlin gunmen seized and raised the Russian flag over Crimea's parliament and government buildings on Wednesday.
Ukraine's bloodiest crisis since its 1991 independence erupted in November when Yanukovych made the shock decision to ditch an EU trade pact in favour of closer ties with old master Russia.
The 63-year-old fugitive issued a statement to Russian news agencies from an undisclosed location on Thursday announcing that he was "compelled to ask the Russian Federation to ensure (his) personal security."