Ukraine sent an elite national guard unit to its southern port of Odesa, 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 Kyiv intensified its attempts to bring both regions back under its control, but seemed particularly alarmed by the bloodshed in Odesa. 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 neighbouring Moldova, another former Soviet republic, where the government said late Monday it had put its borders on alert. Moldova's breakaway Trans-Dniester region, located just northwest of Odesa 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 Odesa — in addition to a swath of industrial eastern Ukraine — would be catastrophic for the interim government in Kyiv, 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, Odesa 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 Odesa are well-educated and understand perfectly well that Russia is sowing the seeds of civil war and destabilization in Ukraine," said Vladimir Kureichik, a 52-year-old 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 Odesa 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.

Gunfire, explosions in Slovyansk

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 Kyiv.

The Russian Foreign Ministry put the blame squarely on Kyiv, which "stubbornly continues to wage war against the people of its own country." The ministry urged what it called the "Kyiv organizers of the terror" to pull back the troops and hold peaceful negotiations to resolve the crisis.

Ukrainian Interior Minister Arsen Avakov said in a statement that government troops were battling about 800 pro-Russia forces, which were deploying large-caliber weapons and mortars. 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. Five more were killed in fighting in the village of Semenivka.

Both sides indicated fighting was taking place at several sites. An Associated Press crew saw at least four ambulances rushing wounded to a hospital in Slovyansk and one militiaman being carried in for treatment.

Ukrainian National Guard soldiers guard a checkpoint outside of Slovyansk, where heavy fighting broke out on Monday. (Evgeniy Maloletka/Associated Press)

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 Kyiv.

The West has offered billions of dollars in loans to help Kyiv 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 U.S. and up to 1 billion euros from the European Union.

The goal of the pro-Russia insurgency is ostensibly geared toward pushing for broader autonomy, but some insurgents do favour seceding from Ukraine and joining up with Russia.

Buildings seized in a dozen cities

In recent weeks, pro-Russia forces have stormed and seized government buildings and police stations in a dozen eastern cities. Kyiv 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, Odesa had been largely tranquil until Friday, when pro-Ukrainian demonstrators fought back after being attacked by pro-Russian 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, however, echo Putin in describing the region as historically part of Russia. Nearly 30 percent of Odesa's residents identify themselves as Russian.

"We will not become the slaves of NATO and the European Union, and will fight to the end," said Vyacheslav Khrutsky, 45.

Pro-Russia activists gathered at a funeral for a regional member of parliament, Vyacheslav Markin, who died two days after the fire from his burns. Markin was known for speaking out against the Kyiv government.

Activists shouted "Hero! Hero!" and vowed to avenge him.

The city remained calm, however, and Ukrainian flags flew all over the city — unlike in the east, where pro-Moscow groups have replaced them with the Russian tricolor.

Loyalty of Odesa police questioned

The unrest in Odesa brought into question the loyalty of its police force. On Sunday, pro-Russia demonstrators stormed police headquarters and freed 67 people who had been detained in the rioting. Riot police simply stood by and did not interfere.

Mourners grieve at the coffin of Vyacheslav Markin, a regional parliament deputy who died in a fire at the trade union building on Friday, at his funeral in Odesa. (Gleb Garanich/Reuters)

Presumably to prevent police from releasing more prisoners, the Interior Ministry said Monday that 42 others were being sent to another region for investigation.

The Interior Ministry also said it was sending an elite national guard unit from Kyiv to re-establish control in Odesa, and the well-armed officers were seen on patrol.

On the outskirts of Kyiv, 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 by police, working with the national guard and local volunteers.

Police Col. Serhiy Boiko said they were looking for weapons and explosives, but also for printed material that could be used to stir tensions.

The international community has accused Russia of fomenting the unrest in an attempt to destabilize Ukraine and derail the May 25 presidential elections.

On Monday, the Russian Foreign Ministry published a 70-page report listing what it describes as human rights violations by "ultranationalist, neo-Nazi and extremist forces" in Ukraine. The Kremlin wrote that the ministry report "confirms that ... violations of basic human rights in Ukraine have become widespread."

While Putin has made no public comment on Ukraine since the Odesa fire, several Russian politicians have ramped up their anti-Ukraine rhetoric. Russian state media outlets have referred to the fire as genocide.

Relentless Kremlin-driven propaganda campaign

Also Monday, Putin signed into law legislation making it a crime to deny Nazi war crimes or spread deliberately false information about the actions of the Soviet Union during World War II. Those convicted could face up to five years in prison.

The Kremlin has used national pride over the Soviet war victory to consolidate Russian society behind Putin. These patriotic feelings also have figured in a relentless Kremlin-driven propaganda campaign to denigrate the Ukrainian authorities by describing them as fascists and neo-Nazis.

Leaders in Moldova announced its borders were on alert because of concerns about the violence in neighboring Ukraine. President Nicolae Timofti, Prime Minister Iurie Leanca and Parliament speaker Igor Coreman said in a statement that security forces had been ordered "to take all necessary actions to ensure public order inside the country."

They made no reference to any specific threat, but "expressed their concern about the deterioration of the security climate in the region following the escalation of violence in Ukraine," it said, affirming support for Ukraine's territorial integrity.

Russia has said it respects Moldova's territorial integrity, but Moldovan leaders are concerned about unrest in Trans-Dniester, a region controlled by pro-Russian separatists. Moldova has a 1,220 kilometer border with Ukraine.

British Foreign Minister William Hague held talks Monday with Moldovan authorities and said the former Soviet republic should move forward with talks on closer ties to the EU without being seen as a threat to Russia. Hague said Britain is "strongly opposed to any external pressure or any violations of sovereignty and territorial integrity."