An explosion killed two people and wounded 11 on Sunday in Ukraine's government-controlled eastern city of Kharkiv, officials said.

The explosion happened during a pro-Ukrainian march marking the one-year anniversary of the overthrow of the country's former pro-Kremlin president.

The pro-Russian mayor of the town of Kharkiv in eastern Ukraine was in critical condition on Monday after he was shot while riding his bicycle, local officials said.

Gennady Kernes was "hit by a bullet in the back" during an attack by an unidentified gunman, a town hall official said. "He is being operated on. Doctors are fighting for his life."

Ukraine faced a fresh secessionist crisis Monday when pro-Russians occupying the Donetsk government seat proclaimed independence from Kiev and vowed to hold a referendum on joining Kremlin rule.

The declaration and subsequent appeal for Russian military help should Kiev's new pro-Western leaders resist their independence drive put the nation of 46 million in danger of disintegration and added still more pressure on Western powers to act.