In some ways, the investigation will mirror the search for the Malaysia Airlines flight that went missing in March, when Malaysia had jurisdiction and other countries assisted.

The US National Transportation Safety Board, which often investigates air accidents overseas and must be invited to join, said it was still determining its possible involvement in probing the Ukraine loss.

"We are communicating with other government agencies and evaluating what our role will be," the agency said in a statement.

US and European air regulators warned in April that airlines should avoid flying over the Crimean Peninsula and parts of Ukraine.

However, some airlines were routinely flying over the northern part of Ukraine, said Mark Duell, vice president of operations at FlightAware.com, a flight-tracking website.

Lufthansa AG, Air India and Malaysia Airlines are among the airlines that have flown there, according to FlightAware's data.

"It doesn't seem anyone's been avoiding Ukraine," Duell said. "I don't see airlines going over Crimea, but I don't see anyone avoiding the rest of Ukraine."

However some international airlines, including Australia's Qantas Airways and Korea's two major carriers, said on Friday that they had already shifted routes to avoid Ukrainian air space due to the conflict between Kiev and pro-Moscow rebels.

Cohn said he expected regulators to issue broader warnings about Ukraine airspace, and that airlines would be more cautious in the area even if regulators did not expand such warnings.

China's civil aviation authorities on Friday ordered Chinese aircraft flying over Ukraine to avoid the country's eastern airspace, Xinhua reported.

On Thursday, the Federal Aviation Administration said US airlines "have voluntarily agreed not to operate in the airspace near the Russian-Ukraine border".

"The FAA is monitoring the situation to determine whether further guidance is necessary," the agency said.

Several airlines, including Turkish Airlines, have since announced they would avoid Ukrainian airspace.

Malaysia Airlines plane crashes in Ukraine	Top Dutch AIDS expert on Malaysian plane