President Volodymyr Zelensky on Sunday urged foreigners to head to Ukrainian embassies worldwide to sign up for an "international brigade" of volunteers

to help fight invading Russian forces.

"All foreigners wishing to join the resistance against the Russian occupiers and protect global security are invited by the Ukrainian leadership to come to our state and join the ranks of the territorial defence forces," Zelensky said in a statement.

"A separate unit is being formed from foreigners -- the International Brigade of the territorial defence of Ukraine. This will be a key testimony of your support for our country."