Ukraine's UN Ambassador Yuriy Sergeyev declared on Friday that his country was strong enough to defend itself as he accused Russia of illegally sending military planes and attack helicopters across the border of the former Soviet republic.
Sergeyev was speaking to reporters after briefing the UN Security Council in a closed-door session on the escalating crisis in Ukraine.
"We are strong enough to defend ourselves," he said outside the council chamber.
Armed men took control of two airports in Ukraine's autonomous Crimea region earlier on Friday in what the country's leadership described as an invasion and occupation by Russian forces. Russia denied involvement in the airport seizures.
Ukraine had asked Lithuania, the president of the Security Council for February, to schedule Friday's meeting of the 15-nation body.
"Due to the deterioration of the situation in the Autonomous Republic of the Crimea, Ukraine, which threatens territorial integrity of Ukraine ... I have the honour to request an urgent meeting of the Security Council in accordance with Articles 34 and 35 of the UN Charter," Sergeyev wrote to Lithuanian Ambassador Raimonda Murmokaite.
Article 34 of the UN charter talks about the power of the 15-nation council to investigate disputes or "international friction" to determine whether international peace and security is in jeopardy.
Sergeyev told reporters there was an "external presence" in Crimea that was "encouraging separatism." He said he had informed the council about "unspecified and armed forces of the Russian Federation on the territory of Ukraine."
"We informed about the illegal crossing (of) the borders by Russian military transport aircraft IL-76, around 10 of them," he said, adding that 11 Russian Mi-24 military attack helicopters had also violated the Russian-Ukrainian border.
It was not clear what the council could do at the meeting. Russia is a veto-wielding permanent member of the Security Council and, therefore, able to block any proposed action by its members.
"I can't see Russia allowing this council to do anything in the way of condemning (ousted Ukrainian President Viktor) Yanukovich or what appears to be its own actions in Ukraine," a Western diplomat told Reuters.
Russian Ambassador Vitaly Churkin, who council diplomats said had wanted to delay the meeting to Saturday at the earliest, was asked on the way in what he thought the meeting would achieve.
"I have no idea," Churkin said.
British Ambassador Mark Lyall Grant said the meeting was "an important opportunity to set out our concerns about developments particularly in the Crimea, also to call on all parties to de-escalate the situation and reduce the tension."
Lyall Grant said it was a good chance "to underline the importance we hope all member states attach to the unity and territorial integrity of Ukraine."
Russia has criticized Ukraine's new government and voiced support for Yanukovich.
The Ukrainian letter to Lithuania's UN ambassador came hours after Ukraine's parliament said it would appeal to the council to call a session to consider the problems in Ukraine in the light of a 1993 understanding in which the big powers agreed to guarantee Ukrainian territorial integrity.