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.

Syrian opposition figures met in Moscow on Monday as part of a new Russia-coordinated bid to wind down the war in Syria, although there was little hope of a breakthrough.

The main opposition group, the exiled National Coalition, has boycotted the talks while Syrian President Bashar Assad cast doubt on the Moscow initiative bearing any fruit.

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.

Syrian opposition figures on Monday began four days of talks on how to end the near four-year conflict, with members of President Bashar Assad's regime set to join them but the main exiled opposition alliance boycotting the event.

The closed-door talks opened as planned at 11 am Moscow time (0800 GMT), a Russian diplomatic source told RIA Novosti. The talks are set to run until Thursday.

A major offensive in eastern Ukraine by rebels allegedly backed by Russia has marked a dangerous new stage in the nine-month conflict and dashed hopes for a truce, pressuring Western nations to act.

A deadly rocket attack on the port city of Mariupol on Saturday highlighted a week-long rebel advance that has seen the separatists take the long-disputed Donetsk airport and pledge to conquer more territory.

U.S. President Barack Obama vowed on Sunday to ramp up pressure on Russia after rocket attacks blamed on Kremlin-backed Ukrainian rebels killed 30 and injured 95 more.

Saturday's surprise assault on the strategic eastern Ukrainian port of Mariupol threatened to open a new front linking separatist territory near the Russian border with the Black Sea peninsula of Crimea that Moscow annexed in March.

The Syrian ambassador to the United Nations, Bashar Jaafari, will head the government team in peace talks due to open in Moscow on Monday, a pro-government newspaper reported.

But the delegation will not join the talks until Wednesday, after two days of preliminary discussions among opposition participants, the Al-Watan newspaper reported.

U.N. Secretary-General Ban Ki-moon condemned a deadly rocket attack in Ukraine's government-held port of Mariupol on Saturday and denounced "provocative statements" made by pro-Russian separatist fighters.

Ban's remarks came after pro-Kremlin rebels announced a major new offensive and heavy rocket fire killed at least 30 people and wounded around 100 in Mariupol, a strategic port linking separatist territory with Russian-occupied Crimea.

U.S. Secretary of State John Kerry on Saturday called on Russia to "immediately" stop backing Ukrainian separatists after at least 30 people were killed in the strategic port of Mariupol in a major escalation of the fighting in eastern Ukraine.

"We call on Russia to end its support for separatists immediately, close the international border with Ukraine, and withdraw all weapons, fighters and financial backing," Kerry said during a visit to Zurich.

Pro-Kremlin rebels announced a major new offensive on Saturday after heavy rocket fire killed at least 30 people in a strategic government-held Ukrainian port linking separatist territory with Russian-occupied Crimea.

The local mayor's office said 97 people were also wounded in the city of Mariupol by dozens of long-distance rockets that smashed into a packed residential district early in the morning and then again shortly after noon.