The Free Syrian Army will shun the planned Geneva peace conference and pursue its fight to topple President Bashar al-Assad regardless, the rebels' commander has said.

The stance of the FSA's General Salim Idriss on Tuesday highlighted the difficulty for international mediators to get Syria's divided parties to the negotiating table in Switzerland on January 22.

The UN said on Monday that the goal of the Geneva II talks was an agreement for a transitional government to end the conflict, which has raged for more than two years and killed more than 100,000 people, while displacing millions more.

"Conditions are not suitable for running the Geneva II talks at the given date and we, as a military and revolutionary force, will not participate in the conference," Idriss told Al Jazeera.

"We will not stop combat at all during the Geneva conference or after it, and what concerns us is getting needed weapons for our fighters."

The diplomacy has brought no let-up in the violence. A suicide bomber killed 15 people and wounded more than 30 at a bus station in a suburb west of Damascus on Tuesday, state media and the Observatory for Human Rights said.

Heavy fighting has raged for days outside the capital Damascus and the northern city of Aleppo, with rebels reporting small gains after months of losing momentum to Assad's forces.

The only solution that allows us at once not to have Mr Bashar al-Assad. Laurent Fabius, French foreign minister

Assad, emboldened by a string of military successes, has said he will send delegates to the Geneva talks but will accept no preconditions and will put any agreement to a referendum - a vote which opposition figures say will be rigged against them.

The Western-backed FSA is an umbrella group encompassing many rebel units, but opposition sources and analysts say its influence has already been eroded by groups forging alliances among the most powerful rebel forces.

SNC chief Ahmad al-Jarba said earlier on Tuesday the group had yet to make a final decision yet on whether it will take part in the Geneva II peace conference, but his group had indicated its desire to go.

"We think that the Syrian regime is the one which doesn't want to go to Geneva II, but the Russians are putting pressure on them to attend," Jarba said.

He said the international community must prove its seriousness by forcing Damascus to agree on trust-building measures.

Laurent Fabius, the foreign minister of France, said January's peace summit would take place without the presence of Assad or radical opposition groups.

"The purpose of Geneva II is not to have an armchair discussion about Syria, it's to have mutual agreement between regime representatives - without Assad - and the moderate opposition in order to form a transitional government," Fabius told French radio.

"It's very difficult, but it's the only solution that allows us at once not to have Mr Bashar al-Assad and not to have the terrorists," he said, referring to extreme members of Syria's opposition.