The Lebanese Cabinet has yet to approve a United Nations plan for a tribunal to try those accused of assassinating the former premier, a strong critic of Syrian influence in the country.
Neighboring Syria, implicated in a UN report in the car bombing that killed Hariri two years ago, has denied involvement.
"We have certain reservations about this tribunal, because we are wondering whether it will strengthen stability and normalize the situation in Lebanon or cause a new upheaval in the country," said Alexander Saltanov after a meeting with Lebanese Prime Minister Fuad Siniora.
Lebanon, divided between the largely pro-Syrian Muslim Shiite majority led by Islamist group Hezbollah and the Christian minority opposed to Syrian influence, survived a 15-year civil war that ended in 1990.
Last summer, the country was devastated by Israeli air strikes during the IDF's campaign against Hezbollah, and at the end of the year Hezbollah-inspired mass rallies were held demanding the government's resignation.
Russia, which maintains contacts with all Arab countries and was opposed to the U.S.-led invasion of Iraq in 2003, portrays itself as a "delicate" moderator in the turbulent region.
Rafiq Hariri was one of the five high-ranking Lebanese figures to be assassinated over the last two years in a series of murders that included Lebanese Christian Cabinet Minister Pierre Gemayel in November.