Last Updated May 2, 2014 11:35 AM EDT
SLOVYANSK, Ukraine -- Pro-Russia forces shot down two Ukrainian helicopters Friday and Ukraine reported "many" rebels dead and wounded as the interim government in Kiev launched its first major offensive against an insurgency that has seized government buildings across the east.
The Kremlin said Kiev's offensive against the insurgents "destroyed" the two-week-old Geneva agreement on cooling Ukraine's crisis.
Fighting broke out around dawn near Slovyansk, a city 100 miles from the Russian border that has become the focus of the armed insurgency. Two helicopter crew members were killed in the crashes, both sides said, and pro-Russia militiaman was reported killed.
Acting President Oleksandr Turchynov said two Ukrainian soldiers were killed and seven wounded in Friday's clashes and the insurgents suffered significant losses, including many killed and injured. By early evening, he said the army now controlled all of the checkpoints around Slovyansk.
One of the helicopters was hit by a surface-to-air missile, the Ukrainian Security Service said, adding that the sophisticated weapon undercut Russia's claims the city was simply under the control of armed locals. The service said its forces were fighting "highly skilled foreign military men" in Slovyansk.
One wounded helicopter pilot was seen in a Rossia 24 television video as being in the hands of pro-Russia forces.
Central Slovyansk still remained in the hands of pro-Russia gunmen, according to AP journalists in the city. Several foreign news crews were detained for several hours Friday before being released.
Television crews from CBS News and Sky News were detained Friday on the outskirts of Slovyansk.
CBS News correspondent Clarissa Ward told "CBS News This Morning" that she and her crew were stopped by pro-Russia insurgents at a checkpoint just outside Slovyansk, then taken to a nearby town where they were blindfolded tightly with masking tape. They were released several hours later, unharmed except for one crewmember who was beaten.
Ward said the militants separated the men from the women and, while keeping them blindfolded, interrogated them about their nationalities and asked whether they had families. A veteran war correspondent, Ward said that when questions like that are asked, "you start to feel a pit in your stomach."
A clash also broke out late Friday between pro-Russians and government supporters in Odessa, on the Black Sea coast 330 miles from the turmoil in the east. Police said one person died from gunshot fire and other was wounded. Odessa had remained largely untroubled since the February toppling of pro-Russia President Viktor Yanukovych, which ignited tensions in the east.
Turchynov admitted earlier this week that the central government had lost control of the east, where some government troops and police were "either helping or cooperating with terrorist organizations." He said forces were working to prevent the unrest from spreading to central areas like Odessa.
In Moscow, Russian President Vladimir Putin's spokesman said the Ukrainian offensive "effectively destroyed the last hope for the implementation of the Geneva agreements" that aimed to defuse the crisis. But Dmitry Peskov said Russia "continues to undertake consistent efforts on de-escalation."
A day earlier Putin warned Ukraine not to move against the insurgents and said it should withdraw its military from eastern and southern regions.
Ukraine, a nation of 46 million, is deeply divided between those in the west who favor closer ties with Europe and many Russian-speakers in the east who look toward Moscow. Ukraine has accused Russia of backing the insurgents who have seized government buildings in 10 eastern cities and fears that Moscow is seeking a pretext to invade; Russia has already stationed tens of thousands of troops in areas near the Ukrainian border.
Russian troops backed separatists in Ukraine's Black Sea peninsula of Crimea in March, then annexed the region after a referendum called for secession.
The deal in Geneva last month aimed to get those who had seized government buildings in Ukraine to leave and calm down the tensions that have prompted the United States and the European Union to slap Russia with rounds of sanctions.
On Friday, President Barack Obama said the U.S. and Germany are preparing to impose sanctions on Russia's economic sectors if destabilization continues in Ukraine. Mr. Obama said he hopes not to have to use such sanctions, but will if Russia's disruptions threaten Ukraine elections scheduled for May 25.
Russia's foreign ministry accused Ukraine's fledging government of using "terrorists" from ultranationalist organizations for the military operation. It also claimed that Kiev deployed tanks and helicopters that were "conducting missile strikes on protesters," something that neither side in Ukraine reported.
An Associated Press crew also saw no evidence of missile strikes in Slovyansk.
Russia also cited insurgents in Ukraine as saying that some of the government attackers spoke English.
Ukrainian troops met fierce resistance Friday morning but managed to take control of nine checkpoints on the roads around Slovyansk, Interior Minister Arsen Avakov said in a statement. He called on the insurgents to lay down their arms and release their hostages.
"We are ready to negotiate with protesters and their representatives," Avakov said. "But for terrorists and armed separatists, there is only punishment."
Earlier in the day, Slovyansk appeared quiet but empty and tense and an AP reporter saw six Ukrainian armored vehicles on a road into the city. Black plumes of smoke could be seen on the edge of the city and residents said emergency sirens had sounded at dawn.
The spokesman for the military wing of the pro-Russia forces, who would give only his first name, Vladislav, said fighting had broken out at several points around Slovyansk and said Ukrainian troops had made incursions into the city itself. That claim could not be independently confirmed.
Peskov said the Kremlin had sent envoy Vladimir Lukin to Ukraine's southeast to negotiate the release of seven foreign military observers among those being held hostage by pro-Russia militia in Slovyansk.
Kiev's interim government came to power after Yanukovych fled to Russia in February, drummed out by months of anti-government protests.