US secretary of state John Kerry has warned Russia against its plan to provide Syria with long-range surface to air missiles, saying it would jeopardise any attempt to hold peace talks.

Mr Kerry made the comments at a news conference with Germany's foreign minister, Guido Westerwelle, ahead of a preparatory meeting in Geneva next week on a joint US-Russian bid for talks to end Syria's two-year civil war.

"It is not helpful to have the S-300 [air defence missiles] transferred to the region while you are trying to organise this peace," he said.

"It is not helpful to have a lot of other ammunition and other supplies overtly going in not just from the Russians – and they are supplying that kind of thing – but also from the Iranians and Hezbollah."

Mr Kerry says the delivery of missiles would have a "profoundly negative impact" on the balance of interests and the stability of the region.

Syria's president Bashar al-Assad suggested this week that his government has already received the S-300 missiles.

Key points: John Kerry says Russia's plan to provide Syria with long-range missiles would jeopardise any attempt to hold peace talks

John Kerry says Russia's plan to provide Syria with long-range missiles would jeopardise any attempt to hold peace talks Mr Kerry says supplying the missiles would endanger a joint US-Russian initiative for a peace conference in Geneva

Mr Kerry says supplying the missiles would endanger a joint US-Russian initiative for a peace conference in Geneva Syrian troops along with Hezbollah allies continuing their assault on the strategic town of Qusayr

Syrian troops along with Hezbollah allies continuing their assault on the strategic town of Qusayr United Nations Security Council adds Syrian rebel group Jabhat al-Nusrato to a sanctions blacklist because of its links to Al Qaeda in Iraq

But Russia's Vedomosti and Kommersant newspapers rejected the claim, saying Moscow may not deliver the missiles this year.

Russian news agency Interfax reported that Moscow could also supply 10 ultra-modern MiG-29 fighter jets to Syria under a possible contract being discussed with Damascus.

On Friday, the European Union [EU] formally waived the arms embargo against rebels, leaving members free from June 1 to decide at their discretion whether to supply carefully vetted weapons to the opposition.

But there was a joint commitment to refrain from supplying weapons "at this stage" for fear of endangering a US-Russian initiative for a peace conference in Geneva, with a review of this due "before August 1".

The United States hopes that with Russian support it can convene talks leading to a political solution to the bloody stalemate in Syria, which threatens to ignite unrest in neighbouring countries.

But in an interview with Hezbollah's Al-Manar television broadcast Thursday, Mr Assad said he was "very confident" of victory against the uprising, in which more than 94,000 people have been killed.

The Syrian rebels meanwhile remain deeply divided, and have vowed to boycott all peace talks until Hezbollah withdraws from the country.

Fighting rages in Qusayr

The developments come as Syrian troops, along with Hezbollah allies, continued their assault on the strategic town of Qusayr.

Syrian state television said troops and Hezbollah fighters captured the northern district of Arjun in Qusayr on Thursday, leaving rebels little chance to escape.

Syria's opposition said hundreds of rebel reinforcements, most close to the Muslim Brotherhood, have now reached Qusayr.

George Sabra, the interim leader of the National Coalition, said about "1,000 fighters from across Syria" had penetrated the rebel stronghold near the Lebanese border.

The Syrian Observatory for Human Rights opposition group says hundreds of rebels broke through army lines near Shamsinn, north-east of Qusayr, after losing 11 fighters.

The UN's refugee agency says thousands of people who have fled the besieged town are in dire need of aid, as its tally for Syrians who have escaped their war-torn nation topped 1.6 million.

Meanwhile, the United Nations Security Council has added the Syrian rebel group Jabhat al-Nusrato to a sanctions blacklist because of its links to Al Qaeda in Iraq.

The sanctions imposed on the hardline Islamist group include an assets freeze, travel ban and arms embargo.

The Al Nusra Front has emerged as one of the most effective rebel forces in the Syrian conflict.

Last month, its leader announced the group's allegiance to Al Qaeda.

ABC/AFP/Reuters