An inquiry into the radiation poisoning of a former Russian spy opened Tuesday with claims that there may have been an earlier assassination bid in the most sensational tale of espionage since the Cold War.

Alexander Litvinenko was killed -- apparently via a cup of green tea laced with hard-to-detect polonium-210 -- in an upmarket London hotel in 2006.

European Union leaders on Tuesday threatened new sanctions against Russia over a bloody offensive by pro-Kremlin Ukrainian rebels, backing, the latest bid to pressure a defiant President Vladimir Putin.

The decision came a day after Standard and Poor's downgraded Russia's foreign currency rating to junk because of its eroding economic health, weakened by a wave of Western financial restrictions last year and the plunging price of its oil exports.

Fighting in east Ukraine over the last 24 hours has killed at least nine soldiers and wounded 29, the military said Tuesday, as rebels fought to secure more territory in the war zone.

The U.N. said Monday that a rocket attack that killed 30 people in a city in eastern Ukraine deliberately targeted civilians, as Russian President Vladimir Putin spurned Western calls to rein in a pro-Moscow insurgency.

A senior U.N. official told an emergency Security Council meeting that the deadly rocket barrage on the port city of Mariupol came from pro-Russian rebel-controlled territory and sought to strike a civilian population, in violation of international humanitarian law.

A rocket attack on the Ukrainian city of Mariupol that killed 30 people at the weekend deliberately targeted civilians and the perpetrators must be brought to justice, a senior U.N. official said Monday.

U.N. Under Secretary-General Jeffrey Feltman told an emergency Security Council meeting that a crater analysis by European monitors showed the rockets were fired from territory controlled by pro-Moscow rebels.

Masked Russian riot police on Monday raided the office of a television channel serving Crimean Tatars, a minority ethnic group in Crimea that opposed Moscow's seizure of the peninsula from Ukraine last year.

In a move the Organization for Security and Cooperation slammed as "intrusion" against the freedom of the media, dozens of armed masked men searched the headquarters of the ATR channel in the regional center Simferopol, seizing servers and other equipments.

President Vladimir Putin on Monday ridiculed the Ukrainian army as NATO's "foreign legion", ignoring Western pressure on the Kremlin to rein in a pro-Russian insurgency that has gone on the offensive across eastern Ukraine.

Putin's comments came as an emergency meeting of the Western alliance's NATO-Ukraine Commission was called to discuss a surge in fighting that has led to a spate of civilian casualties and rapidly growing pressure on Ukraine's troubled military.

Nearly 500 coal miners in Ukraine's war-torn east were briefly trapped underground on Monday after their pit lost power when a shell hit an electricity substation.

The incident occurred in rebel-controlled Donetsk city's Zasyadko coal mine -- one of eastern Europe's largest and scene of a similar incident on January 11.

Ukrainian authorities rushed to evacuate children from parts of the war zone Monday in the wake of a deadly rocket attack on the port city of Mariupol and as fresh clashes hit the country's east.

Another nine people were reported killed, including seven soldiers, as Kiev accused pro-Russian rebels of firing more than 100 times over the past day on both Ukrainian military positions and civilian areas.

French President Francois Hollande held talks with his Ukrainian counterpart Petro Poroshenko and European Council chief Donald Tusk on Sunday to express his "very strong concern" over the surge in violence in eastern Ukraine, the presidency said.

It added that Hollande was also due to speak with Russian President Vladimir Putin and German Chancellor Angela Merkel on Monday to discuss the escalation of fighting, after heavy rocket fire killed 30 civilians in the strategic port of Mariupol on Saturday.