Pro-Russian rebels have shot down two Ukrainian ground attack jets in eastern Ukraine, a Ukrainian military spokesman has said, just days after the downing of Malaysia Airlines flight MH17.

"Two Sukhoi Ukrainian fighter jets have been shot down. The fate of the pilots is not known," spokesman Oleksiy Dmytrashkivsky said on Wednesday, adding that the planes were brought down about 25km from the crash site of MH17.

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But a second military spokesman said the jets had been shot down at a different location and that the pilots managed to parachute out, he said.

"Today in the south of the Luhansk region close to the village of Dmytrivka, pro-Russian fighters shot two Su-25 jets from a missile system," spokesman Vladislav Seleznev said.

"The pilots took evasive action ... but the planes were hit," he said.

The latest action comes as the remains of 40 victims from MH17 were flown from eastern Ukraine to the Netherlands.

A Dutch military aircraft took off first from the airport in the government-controlled city of Kharkiv bound for Eindhoven. It was followed an hour later by an Australian army transport plane.

The first flight touched down at about 1.45pm GMT, as flags flew at half-staff on a day of mourning across the nation, which lost 193 citizens in the flight that was allegedly shot down.

Speaking from Eindhoven, where the bodies will arrive, Al Jazeera's David Chater said all of the bells of the Netherland's churches would ring, and a trumpet would be played as the plane lands.

US officials said the Malaysia-bound plane from Amsterdam was mistakenly shot down by pro-Russian separatists.

Investigators hoped two flight recorders, which have been recovered from the crash site and sent to Britain for analysis, would help to shed light on the disaster that killed all 298 on board.

Evidence gathered by US intelligence officials suggests pro-Russian separatists launched the SA-11 surface-to-air missile that blew up the Malaysia Airlines flight on Thursday, but it remains unclear "who pulled the trigger" and why.

Source: Al Jazeera and agencies