Ukraine security services on Friday announced the launch of a "terrorism" probe after the explosion of a homemade bomb outside the Kiev offices of Russia's state-controlled Sberbank the previous day.

The explosion, which caused no injuries but shattered nearby windows, was the first of its kind in the Ukrainian capital.

Turkey said Friday it will send and "informal mission" to Crimea to monitor what it termed the "oppression" of Crimean Tatars, an ethnic group that opposed Russia's 2014 seizure of the Black Sea peninsula.

"We are sending an informal mission to observe the human rights violations in Crimea soon," Turkey's Foreign Minister Mevlut Cavusoglu told reporters in Lithuania.

Russian diplomats involved in the historic framework accord limiting Iran's nuclear program said Friday Moscow's atomic energy agency, Rosatom, was ready to provide Tehran with new reactor fuel and process spent rods.

"The Russian Federation and Rosatom are ready to supply new fuel and process irradiated fuel in existing reactors, and those Iran will be building," said Russian Deputy Foreign Minister Sergei Ryabkov according to Russia's Interfax press agency.

With heavily-armed men patrolling the streets, shootings in the dark of night and the echo of gunfire from the airport, life is far from normal in the east Ukraine city of Donetsk weeks after the signing of a ceasefire.

On a day like any other, huge trucks transporting armored vehicles ply the streets, pro-Russian rebels tooled up with Kalashnikovs and ammunition browse supermarket aisles and vehicles are pulled up at checkpoints to be searched before entering town.

Ukraine's beleaguered forces have faced problems all of their own making as they've failed to retake separatist territories during a year of conflict -- poor leadership, few supplies, bad coordination.

But the main reason Kiev has struggled to reclaim the rebel regions, some analysts in the West and Ukraine say, is that it has been facing off against thousands of regular Russian troops that Moscow poured in to bolster the insurgency despite blanket denials from the Kremlin.  

Rescuers were on Thursday searching freezing waters off Russia's Far East after a fishing boat sank in the Sea of Okhotsk, possibly after a collision, with the loss of at least 54 lives.

Some 132 people were on board the trawler Dalny Vostok when it went down at around 6:30 am on Thursday (2030 GMT on Wednesday), off the coast of Kamchatka. Sixty-three people were rescued alive. Fifteen people were still missing.

U.S. Secretary of State John Kerry will stay in negotiations with Iran and his counterparts until at least Thursday morning, as they seek to reach a deal on the Iranian nuclear program, Washington said on Wednesday, as Tehran urged global powers to "seize" the moment.

"We continue to make progress, but have not reached a political understanding. Therefore, Secretary Kerry will remain in Lausanne until at least Thursday morning to continue the negotiations," U.S. State Department acting spokeswoman Marie Harf said.

Gulf countries are locked in tough negotiations with Russia on a U.N. draft resolution to impose an arms embargo and sanctions on Yemen, diplomats said Wednesday.

The resolution would seek to re-launch a political dialogue that broke down after Yemen's Shiite Huthi rebels pressed ahead with an offensive, forcing President Abedrabbo Mansour Hadi to flee to Saudi Arabia.

Russia launched Wednesday a probe into tax fraud against a candy factory owned by Ukrainian President Petro Poroshenko and conducted a search of its premises.

Roshen, the company owned by the Ukrainian leader, denounced the raid as illegal, in the latest spat between arch-foes Moscow and Kiev, which is battling a pro-Russian insurgency in its eastern regions.

A close ally of top Kremlin critic Alexei Navalny said on Wednesday he has been given political asylum in Britain after fleeing Russia over alleged political persecution.

Vladimir Ashurkov -- who was executive director of opposition leader Navalny's anti-corruption fund -- told Moscow's independent TV channel Dozhd that British authorities had approved a request he filed last year.