Russia said Wednesday it had approved the candidacy of the former U.S. ambassador to Kiev as Washington's new envoy to Moscow, at a time of sharply heightened tensions over Ukraine.

If he is approved by the U.S. Senate, veteran diplomat John Tefft -- known for backing the pro-Western aspirations of former Soviet states -- will succeed Michael McFaul, who abruptly quit his post in February after just two years on the job.

As a Ukrainian government offensive sends separatists retreating from their strongholds in the country's restive east, there are signs that Moscow is seeking to distance itself from the pro-Russian rebels.

Facing the threat of biting Western sanctions that could further shake Russia's teetering economy, President Vladimir Putin has watched a string of rebel defeats without taking any action -- drawing accusations from separatist sympathizers at home that he is betraying their cause.

Russian Senate speaker Valentina Matviyenko said on Tuesday she abhorred Kiev's "scorched earth" tactics in eastern Ukraine, but that the Kremlin was unlikely to seek a new mandate for military intervention in the crisis.

"What is happening now is a scorched earth tactic, a purge of the territory in certain areas of eastern Ukraine that the National Guard has occupied," said Matviyenko, the speaker of the Federation Council and formally Russia's third most senior politician.

Moscow on Tuesday accused Washington of abducting a Russian national after a man suspected of being one of the world's most prolific traffickers of stolen credit card details was arrested in the Maldives.

The U.S. Justice Department said on Monday that Roman Seleznev had been detained at the weekend.

NATO is drawing up plans to ensure its members can respond more quickly to crises in the aftermath of Russia's "aggression" in Ukraine, the alliance's chief said Monday.

Secretary General Anders Fogh Rasmussen said the transatlantic alliance would review a proposed readiness "action plan" at an upcoming summit in September in Britain and also predicted European members were poised to reverse a long decline in military spending dating back to the Cold War.

Russia on Monday extended by three months the detention of a Ukrainian film director arrested on charges of plotting "terrorist attacks" in Crimea after the peninsula's takeover by Moscow.

"The detention of Oleg Sentsov has been extended until October 11," a spokeswoman for a Moscow court, Yulia Sotnikova, told Agence France Presse.

Retreating pro-Russian insurgents dug in on Monday in Ukraine's sprawling industrial hub of Donetsk after government forces scored a string of morale-boosting victories in the bloody battle for the future of the ex-Soviet state.

The eastern home of one million mostly Russian speakers has been flooded with convoys carrying hundreds of fighters and scores of anti-aircraft guns from five smaller surrounding cities where Ukrainian flags were flying for the first time in three months.

Resurgent Ukrainian forces on Sunday pursued retreating pro-Russian rebels after seizing their symbolic bastion in a morale-boosting win that appeared to dim hopes for a ceasefire in the bloody separatist insurgency.

Western-backed President Petro Poroshenko called the moment when his troops hoisted the Ukrainian flag over the militias' seat of power in Slavyansk "a turning point" in a campaign that has killed nearly 500 people and inflamed East-West ties.

Russian President Vladimir Putin "can be dangerous" and will always push other political leaders as far as he can, former U.S. secretary of state Hillary Clinton told a German newspaper Sunday.

"A man like Putin always goes to the limits. He always tries to find out how strong the others are" and then re-positions himself accordingly, she told Bild am Sonntag.

Russia has barred a leading member of Crimea's pro-Kiev Tatar community from entering his home region for five years after annexing the region from Ukraine in March.

Refat Chubarov, the chairman of the Tatar assembly, or Mejlis, told Agence France Presse on Sunday he had been blocked from crossing into the Black Sea peninsula and handed an official document banning him from Russian territory until 2019.