Ukraine has accused Moscow of 'armed invasion' of Crimea. Ukrainian President's special representative in Crimea, Sergiy Kunitsyn told a local TV channel that 13 Russian aircraft carrying nearly 2,000 suspected troops have landed at a military air base near the regional capital of the restive Crimean peninsula. He added that the air space had been closed.

The UN Security Council has held a brief “private meeting” followed by consultations to discuss concerns about rapidly changing events in Ukraine. Ukrainian Ambassador Yuriy Sergeyev said Russia's expanding military presence in Crimea was a challenge to the security and peace in the region and also a challenge to the territorial integrity of Ukraine.

Meanwhile, US President Barack Obama has expressed deep concern over reported Russian military activity inside Ukraine and warned, “there will be costs” for any intervention. He, however, did not say what those costs might be.