The scruffy rebels who normally populate the headquarters of the rebel Donetsk People's Republic were mostly out of view on Friday. In their place were members of a new faction, who showed up a day before with an armoured personnel carrier and flushed out the occupants.

The separatists' so-called prime minister said nothing has changed — but something has clearly shifted in Ukraine's troubled east.

The balance of power in the east has teetered wildly this week. After Ukrainians elected Petro Poroshenko as the country's president and Russia said it would respect the vote, hopes rose that a resolution was in the works for the conflict between the central government and the insurgents who want Donetsk to be a part of Russia.

But a day later, the rebels launched an exceptionally bold assault, seizing Donetsk's airport. Ukraine's military responded with previously unseen ferocity, launching airstrikes and sending in paratroopers to retake the airport.

To some, the rebel operation looked like a desperate last stand. But on Thursday, rebels shot down a Ukrainian military helicopter, killing 12, including a general. And the same day, the murky Vostok Battalion established themselves in rebel headquarters in the 11-story Donetsk regional administration building, demanding it be evacuated because of what they said was the presence of looters.

The Vostok Battalion's wrath was ostensibly about the ransacking of a supermarket during the battle for the airport, but some interpreted their move as a power grab.

The battalion is believed to consist largely of Russians, bolstering fears among many Ukrainians that Russia is either directing the unrest in the east or supporting it in order to destabilize the country and seize eastern regions bordering Russia.

Donetsk insurgency leaders were at pains to stress that the takeover of their building did not signify a change of guard.

"No coup has taken place. The whole terrible panic that was whipped up over this, what you might call a police operation, is a panic that has been instigated by our so-called friends in Kyiv,"said Alexander Borodai, who calls himself the prime minister of the Donetsk People's Republic.

The heavy contingent of Vostok Battalion militiamen had disappeared by Friday morning, as had the armoured personnel carrier and vintage anti-aircraft gun they arrived with the day before. Inside, however, many members of the militia group were spotted in civilian clothing.

Meanwhile, in Washington, the White House announced that U.S. President Barack Obama plans to meet Wednesday in Poland with Poroshenko, Ukraine's president-elect. Obama's European trip includes a stop in Normandy to attend events marking the 70th anniversary of the Allied landing.

Russian President Vladimir Putin also plans to be in Normandy, but the White House said Obama has no plans for any formal or one-on-one meeting with the Russian leader, even though they will be at the same events.

Also on Friday, the Organization for Security and Cooperation in Europe said it lost contact with a five-member observer team in east Ukraine, where four members of another OSCE mission are still being held by pro-Russian rebels.

The OSCE said in a statement that it lost contact with the team, made up of four international workers and one Ukrainian translator, in the Luhansk region late on Thursday. The OSCE has been out of contact with another four-member team in the neighbouring region of Donetsk since Monday.

An insurgent leader in the Donetsk region confirmed Thursday that members of the first group were in their custody. The rebels told journalists that they would "deal with this and then release them," but didn't elaborate or give a specific timeframe. The OSCE's teams are in Ukraine to monitor the security situation following Russia's annexation of Crimea and the rise of the pro-Russia separatist insurgency in the east.