Kharkiv: Two people were killed in clashes that broke out between pro-Moscow and pro-Kiev supporters in Ukraine`s Russian-speaking city of Kharkiv, police said on Saturday, the second such deadly incident in as many days in the country`s tinderbox east.

One pro-Russia protester and a passerby were killed when Ukrainian nationalists opened fire on a group of men trying to storm their headquarters in the city late on Friday, police sources told AFP.

The deaths were likely to further fuel tensions in the region, coming less than a day after Russia warned that it reserved the right to protect compatriots in the whole of Ukraine.

Police said events leading to the deaths on Friday began when a group of nationalists opened fire from inside a car at a pro-Russian protest being held on Kharkiv`s central Svoboda (Freedom) Square.

No one was reported seriously hurt in the incident and a group of several dozen pro-Russian protesters chased the car, tracking it to the headquarters of the Patrioty Ukrainy (Ukrainian Patriots) nationalist group.

The pro-Russians tried to storm the building and the nationalists opened fire, killing one of them along with a passerby, police said.

The Patrioty Ukrainy group then took several hostages from other offices inside the building as the police arrived, the police sources told AFP.

Six people were injured in the ensuing gunfight, including a police offer who suffered serious wounds.

The nationalists eventually agreed to give up their arms and surrender. Police said they made 30 arrests.

It marked the second death in two days in Ukraine`s tinderbox east, where a pro-Kiev supporter was stabbed to death in the city of Donetsk late on Thursday.

Tensions have spiralled in the region ahead of Sunday`s vote in Ukraine`s southern peninsula of Crime on whether to secede from Kiev and switch to Kremlin rule.