German Chancellor Angela Merkel reiterated a warning Wednesday ahead of a G7 summit that Russia could face new stepped-up economic sanctions if it does not help defuse the crisis in Ukraine.

Hours before the Group of Seven rich countries begins talks in Brussels without Russia, Merkel called in a speech to parliament for stiffer border controls by Russia to stop fighters or weapons crossing into Ukraine.

Vladimir Putin is proving a hard man to snub.

The Russian leader was supposed to be the outcast, booted from the rich nations club and disinvited from the G8 party he was planning in the Olympic City, Sochi, his pride and joy.

Three Ukrainian soldiers have been injured in a massive all-night attack carried out by hundreds of pro-Russian insurgents in the nation's restive east, authorities in Kiev said Wednesday.

The assault on a position held by the Ukrainian National Guard in the Lugansk region began Tuesday evening and lasted 10 hours, the interior ministry said, adding that six rebels were also killed in the fighting.

President Barack Obama met Ukraine's president-elect Petro Poroshenko on Wednesday, in a show of U.S. support for Ukraine's right to chart its own future, before an encounter with Russia's Vladimir Putin.

Obama sat down with Poroshenko in Warsaw, during a trip designed to assuage security concerns in eastern Europe following Russia's annexation of Crimea and what Washington says is an effort to destabilize Ukraine. 

An armed Russian fighter jet intercepted a U.S. military reconnaissance plane in late April in international airspace over the Sea of Okhotsk, several days after another intimidating maneuver in the Black Sea, the Pentagon disclosed Tuesday.

U.S. Defense Secretary Chuck Hagel and the Chairman of the Joint Chiefs of Staff General Martin Dempsey both communicated U.S. concerns over the incident directly to the Russians, Pentagon spokesman Colonel Steven Warren said.

Russia said Tuesday it would not shirk efforts to find a political solution in Syria during its month-long presidency of the U.N. Security Council, calling for a new mediator to be appointed without delay.

Ambassador Vitaly Churkin, under fire from Western colleagues for blocking attempts to enforce humanitarian corridors in the war-torn country, said Moscow wanted a political solution.

The European Union on Tuesday welcomed the new Palestinian unity government as "an important step" in Palestinian reconciliation.

An EU statement hailing its appointment however said future support would depend on the government sticking to principles such as the need for a two-state solution and Israel's right to exist.

U.S. President Barack Obama on Tuesday called on Russia to pressure separatists to stop attacking government forces in eastern Ukraine and to prevent the flow of fighters and weapons into the region.

Obama made the call in a press conference in Poland and also warned that further Russian action in Ukraine could lead to stepped-up economic sanctions.

India is making arrangements to evacuate close to 1,000 nationals, mostly students, from Ukraine's violence-hit Lugansk region, an official said Tuesday.  

"There are around 1,000 nationals, mostly medical students who are being evacuated," foreign ministry spokesperson Syed Akbaruddin told AFP. 

The United States on Tuesday shut its airforce base in Kyrgyzstan that had been the main transit point for military personnel and cargo headed to Afghanistan for 12 years.

Washington was forced to shut the Manas Transit Center north of Bishkek after Kyrgyzstan, an ex-Soviet country seeking closer ties with Moscow, refused last year to extend its lease.