Russian troops and military planes were flowing into Crimea on Monday in violation of accords between the two countries, Ukrainian border guards said.

Over the last 24 hours, 10 Russian combat helicopters and eight military cargo planes have landed on the flashpoint Black Sea peninsula, the guards said in a statement, while four Russian warships have been in the port of Sevastopol since Saturday.

Kiev received no warning regarding the troop movements, even though that is required by the international laws regarding the stationing of Russia's Black Sea navy in Crimea.

Under these agreements, Ukraine should receive notice of any troop movements 72 hours in advance.

Crimea, which has housed Russian navies since the 18th century, has come under control of Russian forces and local pro-Kremlin militia, who have surrounded several Ukrainian military bases.

Ukrainian Defence Minister Igor Tenyukh has accused Russia of sending 6,000 additional troops into Crimea.

On Saturday, Russia's parliament gave President Vladimir Putin the green light to send troops to Ukraine, in a crisis that threatens to escalate into the worst since the Cold War.