NATO Secretary-General Anders Fogh Rasmussen is calling on Russia to "step back from the brink" of war in Ukraine by withdrawing thousands of combat troops massed on its border.

“Step back from the brink, step back from the border and [do] not use peacekeeping as an excuse for war-making,” said Rasmussen during a visit to Kyiv Thursday referring to reports that Moscow may send in troops into eastern Ukraine as “peacekeeping forces.”

Speaking before reporters in Ukraine's capital, he said that Russia, instead of de-escalating the conflict, continues to destabilize Ukraine, and that its support for pro-Russian separatists fighting government forces in the east was growing "in scale and sophistication."

Western analysts say about 20,000 Russian troops have redeployed near the border in recent days, along with armor, infantry, special forces and aircraft.

NATO support for Kyiv

The NATO chief spoke after discussing with Ukrainian officials, including President Petro Poroshenko and Prime Minister Arseniy Yatsenyuk, possible support the Western alliance could offer to bolster Kyiv’s defense capabilities.

Ukraine's President Petro Poroshenko (L) speaks wi
Ukraine's President Petro Poroshenko (L) speaks with NATO Secretary General Anders Fogh Rasmussen during their meeting in Kyiv, August 7, 2014.

In particular, Rasmussen discussed the creation of a NATO trust fund to help boost Kyiv’s defenses in such areas as command and control, communications and cyber defense, Ukraine’s government said in a statement after a meeting between the NATO chief and Ukrainian officials.

The provision of lethal aid by the alliance to Ukrainian armed forces battling pro-Moscow separatists in the country’s east does not appear to have been discussed.

Rasmussen arrived in Kyiv as NATO said Russia had again increased troop levels on its borders with Ukraine to 20,000 and as both the alliance and the United States expressed concern over a possible ground invasion of eastern Ukraine by Moscow in support of pro-Russia rebels. Some sources have suggested that Moscow could send in troops under the guise of “peacekeepers.”

Aeroflot plane instead of MH17?

The head of Ukraine’s Security Service says pro-Moscow rebels had planned to shoot down a Russian Aeroflot passenger plane the day of the downing of Malaysian Airlines flight MH17 to create a pretext for a Russian invasion of eastern Ukraine.

The separatists’ intention was to down Aeroflot flight AFL-2074 which was en route from Moscow to Larnaca, Cyprus, at approximately the same time and in the same air space as flight MH17, which passed over eastern Ukraine June 17, Interfax-Ukraine quoted Valentyn Nalyvaichenko as saying.

Wreckage lies near a pro-Russian separatist checkp
Wreckage lies near a pro-Russian separatist checkpoint at the site of the downed Malaysian airliner MH17 near the village of Rozsypne in Ukraine's Donetsk region August 4, 2014.

Nalyvaichenko said his agency reached the conclusion during the course of its own investigation into the downing of MH17.

He said that the Russian-provided Buk anti-air missile battery which was used to down MH17 had been transferred to Ukraine for that purpose, and that the Aeroflot plane with Russian passengers on board was supposed to have been shot down over territory controlled by Ukrainian government troops.

“This terrorist act, cynically, was planned as a pretext for the launch of an all-out aggression [into Ukraine] in response to the mass killing of innocent Russians,” Nalyvaichenko said.

There has been no immediate reaction from Moscow to the claim.

Rebel leader replaced

One of eastern Ukraine’s rebel leaders, Russian national Aleksander Borodai, announced that a top local separatist will take his place.

Borodai, one of many Russian citizens running the rebellion in eastern Ukraine, told a news conference Thursday that he is appointing Aleksander Zakharchenko as head of the “Donetsk People's Republic,” one of two territorial entities proclaimed by pro-Russia separatists in eastern Ukraine. Borodai said he would now serve as deputy.

Aleksander Borodai (L), leader of the self-proclai
Aleksander Borodai (L), leader of the self-proclaimed "Donetsk People's Republic" shakes hands with rebel leader Aleksander Zakharchenko, during their news conference in Donetsk August 7, 2014.

A native of Donetsk thought to be in his late 30s, Zakharchenko commands a heavily armed rebel unit called “Oplot” (bastion). He was among the first separatists to occupy the regional administration building in Donetsk when pro-Russian crowds captured it in March.

Zakharchenko’s appointment is widely seen as an effort to discredit Western accusations that the rebellion in eastern Ukraine is being run by Moscow.

The Kremlin has been denying involvement in the conflict in eastern Ukraine, laying blame on Kyiv's new government instead.

More fighting

Fighting continued in eastern Ukraine Thursday.  Officials in the city of Donetsk said one person was killed and at least two injured when a city hospital was shelled.  It was not clear who was responsible for the shelling. 

City officials said shelling overnight killed three people and wounded five in another part of the city.  Also Thursday, Ukraine's border guard service reported that Russian forces had fired 46 howitzer rounds at Ukrainian positions across the border the previous day, and that an undisclosed number of border guards were injured.

Additionally, rebel fire downed a Ukrainian fighter jet and a medical helicopter in the same area.  Local reports say the helicopter crew survived and was rescued, while Russia's Interfax news agency said the crew of the fighter jet was later captured.

Some information provided by RFE/RL and Reuters.