Russia said on Thursday the West did not want to commit to a concrete timeframe for a proposed peace conference on Syria because it was not sure the opposition would agree to attend.

In May, Russia and the United States proposed putting together a peace conference in a bid to try to find an end to the civil war in Syria but the date for the talks has repeatedly been pushed back.

At a Group of Eight summit in Northern Ireland earlier this week, the leaders adopted a noncommital statement calling for the peace conference to be held "as soon as possible."

Russian Foreign Minister Sergei Lavrov said Russia pushed for a concrete time frame to be spelled out in the final statement but that its Western partners refused to do so.

"Our Western partners chose not to mention concrete dates because they are not at all sure that they will be able to sell the opposition" (on the need to participate), Lavrov said.

"We offered to define such a timeframe. Let it be a month, two, three, it's not important," he said in televised remarks.

"Our Western partners asked (us) not to do it and as a result, it was written down that there's a need to convene a conference 'as soon as possible'. But we all know what such declarations are worth," he said on the sidelines of the Saint Petersburg Economic Forum.