(Adds report of casualties)
KIEV, April 17 (Reuters) - Shooting broke out overnight near a base of the Ukrainian national guard which came under attack by pro-Russian separatists, Interfax news agency said on Thursday.
It quoted a local online website as saying four people had been killed at Mariupol on the Azov Sea but this could not be independently confirmed, nor were the circumstances of the shooting clear.
It said the shooting broke out after the separatists tried to storm the base. It ended in the early hours of the morning.
Earlier, the interior ministry said in a statement that a crowd of armed protesters arrived at the base and demanded that the national guard troops back their revolt against the country's new pro-Western government.
When the crowd refused to disperse and tried to enter the base, the national guard troops shot into the air, the statement said.
Pro-Russian separatists have taken over buildings in at least 10 cities in Eastern Ukraine, attacks the Ukrainian government has said are orchestrated by Russian agents. The Mariupol city administration is already under the control of separatists.
Russia says the attacks are spontaneous protests by Russian speakers angry at the country's new government, which is more popular in the Ukrainian speaking west of the country. (Reporting by Richard Balmforth and Conor Humphries; Editing by Nick Macfie)