MOSCOW (REUTERS) - The United States is not putting enough pressure on the Syrian opposition to participate in a peace conference Moscow and Washington are trying to organise, RIA news agency quoted Russian Deputy Foreign Minister Sergei Ryabkov as saying on Monday.

"In our view, the United States is definitely not working hard enough in terms of putting influence on Syrian opposition groups so that (they) will come to the international conference," state-run RIA quoted Ryabkov as saying.