Lebanon asked the UN Security Council to set up the tribunal last May amid increasing political turmoil in the country.
"The Russian government has decided to make a one-off contribution of $500,000 to the UN Voluntary Fund for" the Hariri tribunal, Mikhail Kamynin said.
Rafik Hariri, a strong critic of Syrian influence in Lebanon, died in a car bomb in Beirut in 2005. Neighboring Syria, subsequently implicated in a UN report, has denied any involvement in his death.
"We are seeking to have the crime solved, the truth exposed and those guilty brought to justice and punished," Kamynin said.
The UN Undersecretary for Legal Affairs Nicolas Michel announced on Monday the complete formation of the International Tribunal tasked with investigating Hariri's assassination. The Netherlands has agreed to host the tribunal in Leidschendam, a suburb of The Hague.
The UN tribunal will cost $120 million in its first three years. The Lebanese government has agreed to cover 49% of expenses, with UN members volunteering to pay the other 51%. International donors, including the United States, France, Britain, Germany and the Netherlands, have already contributed or pledged to donate $60 million.
Syria claimed on Tuesday it had rejected an offer to freeze the UN investigation into the assassination of Hariri in exchange for 'allowing' presidential polls in Lebanon.
"The court has been used as a political tool," Syrian Foreign Minister Walid Muallem told the Lebanese ANB television channel. "We have an interest in finding out the truth. We want to know the truth."
He did not say who had made the offer to exchange the investigation for polls, but stressed that Syria rejected any political pressure.
"We were told 'facilitate presidential elections [in Lebanon], and we will terminate the tribunal,'" Muallem said.
Lebanon refused to attend an all-Arab summit in Damascus on March 20-30 in protest against Syria's alleged meddling in its internal affairs. The country has been unable to elect a president since November 23 over disputes between the ruling majority and the Hezbollah-led opposition, allegedly supported by Syria. It recently put off, for the 17th time, the country's presidential polls, rescheduling the planned March 25 elections for April 22.
Muallem also said the offer included the imposition of a year-long freeze on the UN court's actions and the financing of the tribunal.
"We do not enter into such bargains," the minister said.
A UN investigation commission said on Friday that a "criminal network" had carried out the 2005 assassination of Hariri and was connected to other acts of political violence in Lebanon. The commission's report did not however identify anyone or any countries involved in the violence.
