British Prime Minister Boris Johnson and Ukrainian President Volodymyr Zelenskyy have agreed on a call that sanctions need to go further to exert maximum pressure on Russia's Vladimir Putin in coming days, a Downing Street spokesperson said on Wednesday.

"The Prime Minister told President Zelenskyy (on call) that the U.K. was rallying UN General Assembly members today, to ensure the strongest possible condemnation of Russia at this afternoon's UN meeting in New York," the spokesperson added.