Kiev

Russian officials said Friday they had arrested three people plotting an attack in the country's south, a week after the assault on a Moscow concert hall killed at least 144 people.

The FSB security agency said it had "put an end to the terrorist activities of three nationals from a Central Asian country", Russian news agencies reported.

Ukraine said Friday that it had imposed emergency blackouts on several regions after Russia fired dozens of missiles and drones at its power stations overnight.

Moscow has stepped up its aerial bombardment of Ukraine in recent weeks, targeting energy infrastructure in response to deadly Ukrainian assaults on Russia's border regions.

Polish Prime Minister Donald Tusk has warned of the "real" threat of conflict in Europe, saying that for the first time since the end of World War II the continent has entered a "pre-war era".

Russia on Thursday blocked the renewal of a panel of U.N. experts monitoring international sanctions on North Korea, weeks after the body said it was investigating reports of arms transfers between Moscow and Pyongyang.

President Vladimir Putin on Monday acknowledged for the first time that "radical Islamists" were behind last week's attack on a concert hall outside Moscow, but suggested they were linked to Ukraine somehow.

Ukraine claimed Sunday to have hit two Russian military ships stationed at the annexed peninsula of Crimea in overnight strikes, as it suffered another night of "massive" Russian aerial attacks.

Four men accused of involvement in a massacre at a Moscow concert hall that killed 137 people were remanded in custody Sunday, as Russia observed a national day of mourning following the attack claimed by the ISIL.

The International Monetary Fund's executive board has confirmed it will disburse $880 million to Ukraine in the third phase of a $15.6 billion aid package to support the country's war-torn economy.

Explosions rang out in the centre of Ukraine's capital on Thursday, following air alerts prompted by Russian missiles and drones, a day after several civilians were killed on both sides of the conflict.

Around ten loud blasts were heard by AFP journalists from 05:00 am (0300 GMT) in Kiev, as well as air defence fire.

EU leaders will grapple at a summit on Thursday with how to get more weapons to Ukraine's outgunned forces while also re-arming their own countries to face Russia's Vladimir Putin — aggressive and newly emboldened after cementing his grip on power.