Russian forces backed by helicopter gunships and armored vehicles Saturday took control of a village near the border with Crimea on the eve of a referendum on whether the region should seek annexation by Moscow, a Ukrainian official said.
Fox News confirmed Russian troops took over a gas installation in the Kherson region, located between Crimea and Russia.
The action in Strilkove appeared to be the first move outside Crimea, where Russian forces have been in effective control since late last month. There were no reports of gunfire or injuries. The incident raises tensions already at a high level before Sunday's referendum.
In a statement, the Foreign Ministry denounced the foray outside Crimea, and said Ukraine "reserves the right to use all necessary measures to stop the military invasion by Russia."
The village is on a long spit reaching northward from the main part of the Black Sea peninsula, about six miles north of the border between Crimea and the Kherson region.
A spokesman for the Ukrainian border guard service, Oleg Slobodyan, told The Associated Press the Russians, about 120 in all, took control of a natural gas distribution station in the village. The Foreign Ministry said the force consisted of about 80 and didn't mention the station, but said the village was seized.
As Crimea prepares for Sunday's referendum, dozens of billboards throughout the regional capital proclaim "Together With Russia." But a few have been hit by spray-painters who scrawled out "Russia" and replaced it with "Ukraine."
The referendum is denounced by Kiev and the West as illegitimate ; the West is threatening costly sanctions against Russia if it moves to incorporate Crimea. But the result is seen as a foregone conclusion -- Crimea is almost certain to vote to split off, further aggravating Ukraine's political crisis and one of the harshest East-West confrontations since the end of the Cold war.
In Moscow, tens of thousands of anti-government protesters marched in central Moscow against the referendum. Protesters carried banners that read: "For your freedom and for ours!" One demonstrator held up a plate of salo -- cured pork fat that is a staple of Ukrainian cuisine and adored by many Russians -- along with a poster that read: "Make salo, not war!"
Nearby, a rally of several thousand people was held close to the Kremlin in support of Russian intervention in Crimea.
At the United Nations, Russia vetoed a Security Council resolution declaring the referendum illegal, and close ally China abstained in a sign of Moscow's isolation on the issue. Supporters of the U.S.-sponsored resolution knew that Russia would use its veto. But they put the resolution to a vote Saturday morning to show the strength of opposition in the 15-member Security Council to Moscow's takeover of Crimea. The final vote was 13 members in favor, China's abstention, and Russia as a permanent council member casting a veto.
The question of whether Crimea, a strategically important Black Sea peninsula that is home to a key Russian naval base, should become part of Moscow's orbit raises strong passions on both sides.
Supporters say the region rightfully belongs to Russia and that the government that replaced fugitive President Viktor Yanukovych is a coterie of fascist-minded nationalists who will abuse Crimea's majority ethnic-Russian population. Opponents bristle at Russia's heavy hand. Crimea effectively is already under Russian control after forces were sent in last month.
Tensions are also high elsewhere in Ukraine.
Two people were killed and several others wounded, including a policeman, in a shootout at the building of a far-right Ukrainian nationalist group, highlighting the tensions in the eastern part of the country that have erupted in Ukraine's political turmoil.
Details of the Friday night shooting in the city of Kharkiv were murky, but local news reports said it broke out after a skirmish between pro-Russia demonstrators and their opponents.
Violence has escalated in Ukraine's Russia-leaning east in recent days, as pro-Russia demonstrators have seized government buildings and clashed with supporters of the new Kiev government. At least one person died and 17 were wounded in clashes in the city of Donetsk on Thursday.
Kharkiv, near the Russian border, is a hotbed of pro-Russia sentiment and opposition to the acting Ukrainian government that took power last month after Russia-friendly President Viktor Yanukovych fled the country in the wake of months of protests.
After the skirmish, according to the reports, there was gunfire outside a building housing the offices of several nationalist groups including Right Sector, which was one of the drivers of the protests against Yanukovych and that vehemently opposes Russian influence in Ukraine.
Russia has denounced Right Sector and similar groups as "fascists" who allegedly want to oppress ethnic Russians in Ukraine.
A spokesman for Right Sector in eastern Ukraine, Igor Moseichuk, was quoted by the Interfax news agency as saying the shooting was a "planned provocation by pro-Russian forces."
Interior Minister Arsen Avakov said on his Facebook page that two people were killed and several wounded, including a policeman who was seriously injured. He said some 30 people "from both sides" had been detained.
The victims' identities were not immediately made public. Moseichuk was quoted as saying the two killed were not among those inside the Right Sector offices.
The Ukrainian region of Crimea, where ethnic Russians are a majority, is effectively under Russian control after troops entered following Yanukovych's departure
The Associated Press contributed to this report.