ODESSA, Ukraine — Ukraine sent an elite national guard unit to its southern port of Odessa, desperate to halt a spread of the fighting between government troops and a pro-Russia militia in the east that killed combatants on both sides Monday.
The government in Kiev intensified its attempts to bring both regions back under its control but seemed particularly alarmed by the bloodshed in Odessa. It had been largely peaceful until Friday, when clashes killed 46 people, many of them in a government building that was set on fire.
The tensions in Ukraine also raised concerns in neighboring Moldova, another former Soviet republic, where the government said it had put its borders on alert. Moldova’s breakaway Trans-Dniester region, just northwest of Odessa and home to 1,500 Russian troops, is supported by Moscow, and many of its residents sympathize with the pro-Russia insurgency.
The loss of Odessa — in addition to a swath of industrial eastern Ukraine — would be catastrophic for the interim government in Kiev, leaving the country cut off from the Black Sea. Ukraine already lost a significant part of its coastline in March, when its Crimean Peninsula was annexed by Russia.
Compared with eastern Ukraine, Odessa is a wealthy city with an educated and ethnically diverse population of more than 1 million. Jews still make up 12 percent of the population of the city, which once had a large Jewish community.
‘‘The people of Odessa are well-educated and understand perfectly well that Russia is sowing the seeds of civil war and destabilization in Ukraine,’’ said Vladimir Kureichik, a literature teacher who left Crimea after it became part of Russia.
The White House said it was ‘‘extremely concerned’’ by the violence in southern Ukraine.
‘‘The events in Odessa dramatically underscore the need for an immediate de-escalation of tensions in Ukraine,’’ said spokesman Jay Carney. He suggested Russia still must follow through with its part of a diplomatic deal aimed at defusing the tensions.
In eastern Ukraine, gunfire and multiple explosions rang out in and around Slovyansk, a city of 125,000 in the Russian-speaking heartland that has become the focus of the armed insurgency against the government in Kiev.
The Russian Foreign Ministry put the blame squarely on Kiev, which ‘‘stubbornly continues to wage war against the people of its own country.’’
Arsen Avakov, Ukraine’s interior minister, said government troops were battling about 800 pro-Russia forces, which were deploying large-caliber weapons and mortars, in Slovyansk. His ministry reported four officers killed and 30 wounded in the fighting.
The pro-Russia militia said at least eight people, both militiamen and local residents, were killed. A spokesman with the militia said that out of 10 people admitted to a hospital in Slovyansk with gunshot wounds, three later died.
This nation of 46 million is facing its worst crisis in decades after its Moscow-leaning president, whose base was in the east, fled to Russia in February following months of street protests. Those eastern regions are now at odds with Ukraine’s western and central areas, which seek closer ties with Europe and largely back the government in Kiev.
The West has offered billions of dollars in loans to help Kiev stave off economic collapse. Prime Minister Arseniy Yatsenyuk said Ukraine expects to receive more than $5 billion in May, according to a government statement Monday. This includes $3 billion from the International Monetary Fund, $1 billion from the United States, and up to 1 billion euros from the European Union.
The goal of the pro-Russia insurgency ostensibly is to push for broader autonomy in the east, but some do favor seceding from Ukraine and joining with Russia.
In recent weeks, pro-Russia forces have stormed and seized government buildings and police stations in a dozen eastern cities. Kiev accuses Moscow of backing the insurgents and fears Russia could use the violence as a pretext to invade. Tens of thousands of Russian troops have been deployed along Ukraine’s eastern border.
But even as violence spread across the east, Odessa had been largely tranquil until Friday, when pro-Ukraine demonstrators fought back after being attacked by pro-Russia groups.
‘‘We feel ourselves to be residents of a free city, Europeans,’’ said Denis Sukhomlinsky, a 34-year-old businessman who took part in the clashes. ‘‘We don’t need the Russian iron hand or the dictatorship of [President Vladimir] Putin.’’
Pro-Russia activists echo Putin in describing the region as historically part of Russia.
On the outskirts of Kiev, checkpoints were set up Monday to control movement into the capital. Cars and buses with out-of-town license plates and other suspicious vehicles were stopped for inspection.