"We value the constructive reaction by the Syrian leadership to the offer" of holding such an international event, Lavrov said, as he welcomed Syrian Deputy Foreign Minister Faisal Muqdad in Moscow.

Lavrov criticized opposition groups and their supporters for undermining the efforts for reaching a solution to end the war.

"So far, every time there is a flicker of hope, we are seeing efforts of well-known forces to ruin any movement forward," he said before talks with Muqdad.

"Among such actions... there is the kidnapping of your father," he told Muqdad, according to Russian news agencies. "This is an unacceptable action by armed opposition. Whether or not it's their goal, it works to undermine efforts to call the conference."

Western-backed militants abducted Muqdad's 84-year-old father Saturday.

"I'd like to highlight that the Syrian regime will always remain a party that strives toward a peaceful solution to the Syria crisis," Muqdad was quoted in Russian as saying. "Unfortunately such efforts don't find any response from those who want to continue violence and bloodshed."

The crisis in Syria began in March 2011, and many people, including large numbers of Syrian soldiers and security personnel, have been killed in the violence.

The Syrian government says the chaos is being orchestrated from outside the country, and there are reports that a very large number of the militants are foreign nationals.

On May 18, President Bashar al-Assad said militants from 29 different countries are fighting against the government in Syria. He stated that foreign intervention is the most important factor aggravating the situation in his country.