Moscow said on Monday that U.S.-led military exercises in western Ukraine that began this week may have "explosive" consequences and threaten to derail the peace process in the separatist east.

"The military drills involving NATO members and Ukraine's army that started in Lviv region under U.S. command are a clear demonstration of NATO's provocative policy to unequivocally support the policies of current Kiev authorities in eastern Ukraine," the foreign ministry said in a statement.

The nomination of a Russian politician to a top post in Odessa has caused a flurry of controversy in the tense political atmosphere of the violent Ukraine conflict.

Maria Gaidar, daughter of former Russian prime minister Yegor Gaidar, was nominated Friday as deputy to pro-Western former Georgian president Mikheil Saakashvili -- who was recently named governor of the southwest Ukraine region of Odessa. 

The landmark deal on Iran's nuclear program that Russia helped steer through marathon talks is a diplomatic fillip for Moscow which will boost trade with Tehran but could also hit much-needed energy revenues, analysts said.

Iran and the P5+1 group -- Russia, the United States, China, Britain, France and Germany -- struck an agreement on Tuesday that would progressively lift economic sanctions against Tehran in exchange for limitations on its nuclear program.

Three civilians and one Ukrainian soldier have been killed over the past day in renewed fighting in the east of the country, where pro-Russian rebels are waging an insurgency, Kiev said on Saturday.

The civilians were killed when the rebels fired on the town of Avdiivka, held by pro-government troops, the interior ministry said, while the army said a soldier died in the neighboring region of Lugansk.

Russia on Friday dismissed constitutional amendments proposed by Kiev to decentralize Ukraine as part of the peace process as merely an "imitation" of compliance.

Ukraine's parliament on Thursday voted in favor of sending to the Constitutional Court a package of reforms that would grant greater autonomy to the war-ravaged separatist east.

A Russian court on Friday authorized the arrest in absentia of the only lawmaker who voted against Russia's annexation of Crimea, in what his supporters say is a politically motivated case.

Ilya Ponomaryov, who currently lives in the United States, has been accused of complicity in the embezzlement of $750,000 from the Skolkovo Foundation, a high-tech project the Kremlin had hoped would be its answer to Silicon Valley. 

Ukraine outraged Russia on Friday by expelling Moscow's top envoy to a vital Black Sea region now governed by the pro-Western former president of Georgia.

The State Security Service of Ukraine (SBU) said Kiev had declared Moscow's consulate general in Odessa "persona non grata" for conducting unnamed activities "incompatible" with his diplomatic work.

Relatives of victims of flight MH17 that was shot down over Ukraine a year ago joined emotional memorials on Friday as calls mounted for a U.N.-backed tribunal to prosecute those responsible for the tragedy.

All 298 passengers and crew -- the majority Dutch -- died on July 17 last year when the Malaysia Airlines Boeing 777, on a flight from Amsterdam to Kuala Lumpur, was downed over rebel-held east Ukraine during heavy fighting between Kiev's armed forces and pro-Russian separatists.

Russian President Vladimir Putin said Thursday that establishing an international tribunal to prosecute those behind the downing of Malaysia Airlines flight MH17 over rebel-held east Ukraine would be counterproductive.

He made his comments in a telephone conversation with Prime Minister Mark Rutte of the Netherlands, whose citizens made up the majority of the 298 people killed in the July 17 disaster last year.

President Barack Obama spoke by phone Wednesday with Vladimir Putin, thanking his Russian counterpart for his role in reaching a deal on Iran's nuclear program.

U.S. ties with Russia have been strained to breaking point over the war in Ukraine, but Russia was an "important" part of the group of nations that negotiated the deal with Tehran.