In the face of western nations calling on Russia to abandon support for Assad, the Russian Foreign Minister, Sergei Lavrov, yesterday emphasised Moscow's strong opposition to external interference.
The decision came as violence surges in Syria, despite a UN ceasefire negotiated in April.
Western powers have held intensive diplomatic discussions with Moscow in recent weeks as the UN Security Council member blocks efforts to have Mr Assad removed by diplomatic means after 15 months of bloodshed.
At a news conference following talks with his Iraqi counterpart, Mr Lavrov said he had seen reports that US State Department spokeswoman, Victoria Nuland, had suggested Washington and Moscow were discussing a post-Assad strategy for Syria.
"If that was really said then it's not true," Mr Lavrov said. "Such discussions are not being held and cannot be held, because to decide for the Syrian people contradicts our position completely.
"We do not get involved in overthrowing regimes – neither through approval of unilateral actions by the UN Security Council nor by participation in any political plots."
Ms Nuland had been asked at a news conference on Thursday whether the US and Russia were discussing a transition of power similar to that seen in Yemen last year, in which President Ali Abdullah Saleh was replaced. "We are continuing to talk about a post-Assad transition strategy in that context," she had said.
Mr Lavrov said any broad international talks must include Iran and must only address ways to create conditions for dialogue in Syria – not its content nor preconditions such as Mr Assad's exit.
Russia, which has come under increasing criticism for arms deals with Syria, responded to US Secretary of State Hillary Clinton's claim that attack helicopters were being delivered.
Mr Lavrov denies making new deliveries of military helicopters to the Middle Eastern state but under old contracts said Russia had repaired craft sent to Syria "many years ago".
"There are no new deliveries of Russian military helicopters to Syria. All arms industry cooperation with Syria is limited to a transfer of defensive arms," the ministry said on its website.
"As regards helicopters, planned repairs of [helicopters] delivered to Syria many years ago were conducted earlier," it said.
A source close to Russia's arms exporting monopoly, Rosoboronexport, said at least nine Mi-25 helicopters were sent to Russia's Baltic exclave of Kaliningrad to be repaired by Oboronservis, owned by the defence ministry.
At least two ships carrying Russian weapons have reportedly travelled to Syria this year, though possibly not on behalf of Rosoboronexport.
Meanwhile, the European Union yesterday banned exports to Syria of luxury goods such as shoes, caviar and boats, as well as items with possible military application.
The move aims to keep up pressure on the family of the Syrian president, in particular his wife Asma al Assad, who is said to have continued shopping for luxury products during the conflict.
And in a bid to encourage a "stronger revolt" against Assad's government, France is considering providing communications equipment to Syrian rebels, its foreign minister said.
Laurent Fabius said France fully supported Arab League-UN special envoy Kofi Annan's peace plan but that it was also looking at "other options."