Col. Yuliy Mamchuk, center, commander of the Ukrainian military garrison at the Belbek airbase, and a colleague with the regimental flag confront troops under Russian command Tuesday. (Sean Gallup/Getty Images)

A tense and dangerous test of wills took place Tuesday on a rainy hilltop at a dilapidated Cold War-era airfield here, as Ukrainian soldiers confronted Russian troops and demanded to be allowed to return to their base.

Just a few hours after the 5 a.m. deadline reportedly issued by Russia’s Black Sea Fleet for Ukrainian troops in Crimea to switch their allegiance from the new government in Kiev to the pro-Russian leadership in Crimea, the first shots of the conflict were fired into the air here by a pro-Russia militiaman.

Russia denied imposing any such ultimatum.

No one was injured in the continuing impasse, but there were tense moments as the two sides faced off, and Ukrainian troops were forced to choose between their oath to Ukraine and their feelings of affinity with Russia.

Video shows the dramatic moments of a tense standoff between Ukrainian soldiers and Russian forces who took control of an airbase in Crimea.

At the Belbek air base, the Ukrainians chose duty.

At the harbor in nearby Sevastopol, a trio of Ukrainian navy vessels spent the night before the ultimatum deadline trapped at a dock as Russian minesweepers and Russian navy tugboats passed back and forth across their bows, blocking their exit.

On Tuesday morning, the Russian rescue and salvage ship Epron cut close to the docks and blasted its klaxon.

Officers of the Ukraine command ship U510 Slavutych said that during the middle of the night, five Russian navy ships from the Black Sea Fleet harassed them, shining search lights at the vessels. The Ukrainian sailors mounted water hoses and mattresses, saying they would repel boarders. They vowed not to surrender their ship.

In addition to the blockade in Sevastopol harbor, Russian navy ships closed off the narrow Kerch Strait, which separates Ukraine’s Crimea Peninsula and Russia, Pavel Shishurin, deputy head of the Ukraine’s border guards, told Reuters news agency.

At the Belbek air base, as Russian snipers assumed flanking positions and aimed their rifles, a column of Ukrainian soldiers marched forward and tried to return to their jobs at the airfield Monday.

The Ukrainians had arrived unarmed.

The Russians were bristling with weapons.

Pro-Russia militiamen and a Russian soldier at Belbek airport Tuesday. (Ivan Sekretarev/AP)

Col. Yuliy Mamchuk, commander of Ukraine’s Sevastopol Aviation Unit, said the Russian troops appeared Thursday and took up positions surrounding the base. On Monday, as the purported deadline to surrender approached, the Russians entered the airfield and forced the Ukrainians out at gunpoint.

“The men felt very bad. They thought they had abandoned their post. We swore an oath to serve,” Mamchuk said.

The Ukrainians were also confused about Russia’s intentions, as the two militaries, especially here on the Crimean Peninsula, had worked closely in the past.

On Monay night, there were rousing, patriotic speeches in the Ukrainian barracks. “We decided we would return to work. Any man who did not want to come, he would not be branded a traitor or a coward,” Mamchuk said. “Every man came.”

The 200 Ukrainians marched back up the hill to tell the Russians they wanted to return to their jobs, to service the airplanes and guard the airfield and warehouse, which was filled with valuable aviation equipment and weaponry.

Their wives accompanied them, but when they saw the snipers, the troops sent the women back.

Mamchuk negotiated with a Russian officer who would identify himself only by the first name “Roman.” The Russians said they needed approval from their superiors to allow the Ukrainians to return to the base.

After no one came, Mamchuk was approached by a member of a civilian self-defense militia from Sevastopol. Mamchuk explained the situation again, though now he was negotiating not with a Russian officer but a Crimean bar owner from nearby Balaklava in mismatched fatigues and black sneakers, who only an hour earlier had been arguing with journalists at the front gate to the base.

He gave his name as Yuriy. Beside him stood another militiaman, his face covered by a black mask.

“I realize this looks like a comedy,” Yuriy said, but it was serious business. He said the people were afraid the Ukrainian airmen would put their planes in the sky and bomb Sevastopol.

Asked about Russian forces behind him, the soldiers still without markings or insignia, Yuriy said he didn’t know anything about them.

The Ukrainian colonel could make no progress. “They’re stalling,” he said. “They’re playing games.”

Ukrainian servicemen march away from the Belbek airport Tuesday. (Vasily Fedosenko/Reuters)

He sent his men back down the hill to their barracks. Asked what would happen next, Mamchuk said: “I am feeling negative. There shouldn't be this kind of escalation with the Russian troops.”

He said the Ukrainians had already sent their children out of Crimea, back to the Ukrainian mainland, after the servicemen and their families started receiving threatening phone calls and text messages.

Asked about the wives, Mamchuk said: “They’re stubborn. They won’t leave us.”