Pro-Russia separatists armed with baseball bats attacked a rally in support of Ukrainian unity in the eastern city of Donetsk on Monday.
A number of people sustained injuries, many of them head wounds after dozens of men dressed in military fatigues tried to disrupt the rally with baseball bats, firecrackers and what appeared to be at least one stun grenade.
Protesters, estimated at about 2,000, waved Ukrainian flags and chanted “Donetsk is Ukraine!” and “Putin No!”. They quickly dispersed after the violence.
In another eastern city, Luhansk, near the Russian border, crowds cheered as one group of activists declared the area an independent state. One of the leaders of the self-proclaimed "Luhansk People's Republic" called on Russia to help it defend its sovereignty.
Earlier on Monday, pro-Russia militants also took another town, seizing the police headquarters and municipal administration building in Kostyantynivka, Donetsk region.
About 20 well-organized gunmen were seen controlling the administration building. They erected a barricade of tires, sandbags and concrete blocks.
Soviet songs played over loudspeakers as women gathered the signatures of people supporting an uprising for independence and possible rule from Moscow.
The mayor of Ukraine's second-largest city, Kharkiv, was in a serious condition on Monday after being shot in the back while riding his bicycle, in the latest violence to strike the eastern part of the country.
Hennady Kernes, 54, traditionally aligned with Russia, was riding along the route he takes almost every day when he was shot, probably by someone hidden in nearby woods, said Iryna Kushchenko, spokeswoman for the local government.
His bodyguards were following in a car but were not close enough to intervene, she said.
The Interior Ministry said Kernes had been taken to the city's hospital for emergency treatment.
“Doctors assess his condition as serious,” the ministry said in a statement.
Kernes was accused by Ukraine's new pro-Western leaders two months ago of promoting separatism when pro-Russian protesters took control of local administrative buildings. He has since softened his stance.
Ukraine's deputy interior minister, Serhiy Yarovy, said investigators are even looking into whether the shooting was in retaliation for the detention in Kharkiv of 13 pro-Russian separatists on Sunday on charges of possession of Molotov cocktails, explosives and nails.
Ukrainian forces evicted pro-Russia activists this month, making Kharkiv the only major eastern city to have taken back control from armed protesters who have demanded a referendum on independence for most of eastern Ukraine.
President Barack Obama announced new sanctions on Monday against Russia for its involvement in the crisis in Ukraine.
The measures are in response to “Russia’s continued illegal intervention in Ukraine and provocative acts that undermine Ukraine’s democracy and threaten its peace, security, stability, sovereignty, and territorial integrity,” said a White House statement, adding that Moscow's involvement in eastern Ukraine violence "is indisputable."
The White House said the targeted sanctions are aimed at a number of individuals and entities and will restrict licenses for certain U.S. exports to Russia.
"The Department of the Treasury is imposing sanctions on seven Russian government officials, including two members of President Putin’s inner circle, who will be subject to an asset freeze and a U.S. visa ban, and 17 companies linked to Putin’s inner circle, which will be subject to an asset freeze," the statement said.
A senior Russian diplomat decisively condemned the new round of U.S. sanctions. Deputy Foreign Minister Sergei Ryabkov said on the ministry's website that the sanctions marked a return to "Cold War" practices.
Separately, the European Union imposed asset freezes and visa bans on 15 more Russians and Ukrainians on Monday.
The decision brings to 48 the number of people that the EU has put under sanctions for, it says, helping undermine Ukraine's territorial integrity.
The names of those to be added to the list will not be made public until they are published in the EU's Official Journal on Tuesday.
Also on Monday, U.S. Defense Secretary Chuck Hagel and Russian Defense Minster Sergei Shoigu held a "candid" hour-long telephone conversation.
Hagel repeated his call for an end to Russia's destabilizing influence inside Ukraine and warned that continued aggression would further isolate Russia and result in more diplomatic and economic pressure.