A Pentagon study from 2008 claimed that Russian President Vladimir Putin has Asperger's syndrome, giving him a need to exert "extreme control" when faced with crises, according to the report released Thursday.

Experts studying his movements and facial expressions in video footage theorized Putin's neurological development was disrupted in infancy, giving him a sense of physical imbalance and a discomfort with social interaction, according to the report by the Pentagon's internal think tank, the Office of Net Assessment.

A mother of seven accused of treason for telling the Ukrainian embassy about Russian troop movements was to be released from jail Tuesday, her husband said, though the charges against her remain.

Svetlana Davydova, who faces between 12 and 20 years in prison, is being held in the high-security Lefortovo jail in Moscow. 

Ukrainian President Petro Poroshenko said on Wednesday he had written a letter to Russia's Vladimir Putin demanding that Moscow rein in eastern separatist fighters in his war-torn ex-Soviet republic.

Poroshenko said his letter also requested that Russia release female Ukrainian pilot Nadia Savchenko, who claims she was abducted by pro-Russian fighters before being put in a Moscow prison and starting a hunger strike.

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.

Russian President Vladimir Putin on Friday accused the Ukraine government of ordering a major new offensive against pro-Russian rebels in the separatist east that has claimed dozens of lives in the past few days.

"Kiev authorities have given an official order to begin large-scale combat operations" along almost the entire frontline with pro-Russian separatists, Putin said in a meeting with his security council.

Russian President Vladimir Putin will visit Hungary on February 17 with controversial Prime Minister Viktor Orban seen as one of his closest European allies.

"We will have bilateral and geopolitical issues on the agenda... including the energy security of central Europe as it is one of the most important issues for the region," Hungarian Foreign Minister Peter Szijjarto told public radio.

Western countries are trying to use the Ukraine conflict to topple President Vladimir Putin and wreck Russia's economy, the president's spokesman said in an interview published on Wednesday.

"In the West they are trying to kick out Putin, to isolate him in international politics, to throttle Russia economically due to their interests, to bring down Putin," Kremlin spokesman Dmitry Peskov said.

Russian President Vladimir Putin has not confirmed his attendance at a crunch peace summit on Ukraine proposed for January 15 in Kazakhstan, the Kremlin said Monday. 

Kremlin spokesman Dmitry Peskov said that Putin's presence at the meeting -- which Ukrainian President Petro Poroshenko hopes will see four-way talks with the leaders of France and Germany -- depends on the outcome of a gathering of foreign ministers in Berlin on Monday.   

Four Ukrainian soldiers and at least as many civilians died Friday in an upsurge of rocket attacks that came just as prospects for international peace talks on the nine-month crisis dimmed.

Local authorities in the rebel stronghold of Donetsk said another nine residents were injured in sporadic clashes that continued from dawn late into the evening around the industrial city's disputed airport.

Thirteen Ukrainian soldiers were killed and 17 injured when the bus they were travelling in collided with military trucks in bad weather in the war-torn east, officials said on Tuesday.

The collision Monday night was due to bad weather and took place during the rotation of professional soldiers and volunteers deployed in eastern Ukraine to fight the pro-Russian rebels who have waged an insurgency against Kiev since April, the National Guard said in a statement.