Russian forces fired warning shots on Ukrainian soldiers at a base near Sevastopol on Tuesday as tensions flared in the standoff over Crimea.
Pro-Russian troops guarding an airfield in Belbek, near Sevastopol, fired the shots in the air as a column of about 300 Ukrainian troops approached around 9:00 am local time, Oleksey Khramov, an officer at the base, told AFP.
"They fired several shots into the air and said they would open fire if they continued to approach," he said.
The Ukrainian soldiers, who were unarmed, then stopped to avoid a confrontation, he said.
In footage of the incident shown on Britain's Sky Television, a pro-Russian soldier told the approaching Ukrainians: "Hold back. I want your officer here! We'll be shooting your legs."
A Ukrainian soldier replied: "You will pay for this, you'll be held responsible."
The Russian soldier told the Ukrainian soldiers to "calm down" and accused them of "deliberately provoking us".
An AFP reporter at the base said the column of troops had since returned inside the administrative base of the Sevastopol tactical aviation brigade in Belbek, where dozens of Ukrainian soldiers are holed up refusing to abandon their posts.
Russian forces have surrounded Ukrainian military bases across Crimea as the Russian-speaking autonomous region has been thrown into turmoil following the ouster last month of Moscow-backed president Viktor Yanukovych.
Tensions are high, but fears of an imminent assault by Russian forces did not materialise overnight.
"The night was quiet," Vladyslav Seleznyov, the defence ministry spokesman for Crimea, told AFP in the regional capital Simferopol.
Ukrainian officials said Monday that Russia had given Ukrainian soldiers in Crimea an ultimatum to surrender or face an all-out assault, although Russia denounced the claim as "complete nonsense".
"No more declarations have been made by the Russian side," Seleznyov said.
In Sevastopol, a bastion of pro-Kremlin sentiment, pro-Russian activists had surrounded the headquarters of the Ukrainian navy in Crimea.
An AFP reporter said about 100 pro-Russia activists were gathered outside the offices and formed a human chain, as Russian forces with automatic rifles stood nearby.
Seleznyov said Russian vessels were also blocking Ukrainian warships from trying to leave the port, which has been the home of the Russian navy's Black Sea fleet for some 250 years.
The Ukrainian defence ministry says several thousand Russian troops have been sent by the Kremlin to Crimea.
Russian President Vladimir Putin on Tuesday denied that Russian forces were operating in Crimea, saying that only "local forces of self-defence" were surrounding Ukrainian military bases.
Armed men believed to be under Moscow's orders last week seized key government buildings in Crimea and airports on the peninsula.
Regional lawmakers deposed the Kiev-supporting prime minister and have called for a referendum on March 30 on proclaiming greater autonomy for Crimea.