Russia's air force struck 32 Islamic State (IS) targets in Syria as Syrian government forces pushed a ground offensive on Thursday, while German Chancellor Angela Merkel called for a political dialogue that includes Russia and international actors.

After 24 hours of flying 33 sorties, the Russian air force has eased the intensity of strikes as the Syrian army has gone on the offensive, Russian Defense Ministry spokesman Igor Konashenkov told the media on Thursday.

"The active offensive operations by the Syrian armed forces have been changing the line of engagement with the IS terrorist groups," the TASS news agency quoted Konashenkov as saying.

The offensive that began before dawn builds on over a week of ground attacks launched with Russian air support in areas of western Syria.

EU leaders met Thursday in Brussels to discuss the refugee crisis that has been becoming increasingly unbearable for the European countries.

Merkel said the conflict in Syria, which borders Turkey, was the biggest cause of the migrant flows to Europe.

"To stabilize the situation in this country, so terribly afflicted by terror and violence, and to bring it peace in the long-term of course we need a process of political dialogue which includes Russia and other international actors, including regional actors," she said.

French President Francois Hollande met with his German and British counterparts on the sidelines of a European summit to exchange views on Syria and seek a common position on the conflict, a French diplomatic source told Reuters on Thursday.

"The idea is to have a common position, also with the view of talks with other partners," the source said, mentioning the next G20 meeting.

Asked if Hollande, German Chancellor Angela Merkel and British Prime Minister David Cameron would launch a common initiative, the source said it was still too early to tell.

"We'll see in the coming days and weeks," the source said.

The atmosphere in the EU summit may not be so friendly with Russia, however.

While leaders will discuss a possible safe zone that Turkey wants to establish on its border with war-torn Syria, European Council President Donald Tusk said, "If we add the fact of the Russian presence and activity in Syria today it shows how difficult this possible safe zone is."

The EU was also set to warn that Moscow's military intervention will only add to the chaos amid concerns millions more people could be forced to flee if the war continues, according to AFP.

"The European Council expressed its concern about the Russian attacks on the Syrian opposition and civilians, and the risk of further military escalation," said draft summit conclusions obtained by AFP.

Russia-US air agreement

As the former Cold War foes conduct air strikes over Syria, the US and Russian militaries met on Wednesday to finalize a memorandum of understanding that sets out basic air safety procedures in the skies above Syria.

The Pentagon said in a short statement that the secure-video conference with Russian defense officials had led to progress in discussions aimed at promoting safe air operations over Syria. It offered no further details.

Russian Defence Ministry spokesman Igor Konashenkov told the media on Thursday that the two countries had come closer to key provisions of a likely agreement on the safety of flights over Syria. Konashenkov remarked that the discussion was professional and constructive, according to TASS.

A US official, who spoke to Reuters on condition of anonymity, said the memorandum of understanding could be implemented in the near future, after a follow-on review.

Also on Thursday, Russian President Vladimir Putin said the US decision not to receive a Russian delegation led by Prime Minister Dmitry Medvedev is "unconstructive."

"I believe this position is unconstructive. The weakness of this stance is based on the apparent lack of any agenda. It seems that there is nothing to talk about," the Russian leader said.

Putin said the delegation might include the top ranking military, such as a deputy chief of the General Staff, and security officers. It was likewise important to work with the countries of the region too, including Turkey, Jordan, the United Arab Emirates, and Iraq, Putin said.