Russia has blocked a draft United Nations Security Council declaration on the situation in the besieged Syrian town of Qusayr, diplomats said Sunday.

The text, proposed by Britain on Saturday, expressed the council's "grave concern" about the fate of civilians trapped in the strategically important town in central Homs province, where regime forces backed by Hizbullah began an assault two weeks ago.

U.S. Secretary of State John Kerry said Friday that Russia's planned delivery of S-300 air defense missiles to Syria is "not helpful" for efforts to convene a peace conference.

Kerry's comments at a news conference with German Foreign Minister Guido Westerwelle came ahead of a preparatory meeting in Geneva next week on a U.S.-Russian bid for talks to end Syria's two-year-old civil war.

Russia could supply 10 ultra-modern MiG-29 fighter jets to Syria under a possible contract being discussed with a visiting delegation from Damascus, Interfax reported on Thursday.

The Russian news agency quoted MiG corporation director general Sergei Korotkov as saying that the details of the contract were now under discussion.

Russia may not deliver a hugely controversial consignment of S-300 air defense missile systems to the Syrian regime this year, two Russian newspapers reported Friday, rejecting claims the weapons had already arrived in the country.

The Vedomosti daily cited a Russian defense industry source as saying it was unclear if the weapons would be delivered to Syria this year while the Kommersant daily quoted its source as saying that delivery was only planned in the second quarter of 2014.

Lebanon should stay out of the Syria conflict and Hizbullah's involvement is "not helping matters", Prime Minister-designate Tamman Salam told French daily Le Figaro in an interview published Friday.

Hizbullah has sent its fighters to help Syrian President Bashar Assad troops recapture the key town of Qusayr near the border with Lebanon.

British Foreign Secretary William Hague said Thursday that Russian weapons supplies to the Syrian regime were impeding the search for a peaceful resolution of the conflict.

"The continued flow of weapons to the (Syrian) regime and the difficulties and disagreements on the attending the Geneva talks don't help at all to resolve this crisis," Hague told journalists here.

The United States said Thursday that Russian arms supplies to Syria's President Bashar Assad "will only prolong the violence" in the war-torn country.

National Security Council spokeswoman Caitlin Hayden declined to comment on Assad's suggestion in an interview to be aired Thursday that his regime has received advanced S-300 air defense missiles promised by Russia.

A top economist has fled Russia after being interrogated over the case of jailed oil magnate Mikhail Khodorkovsky amid fears investigators may be preparing a fresh case against the fallen tycoon.

Sergei Guriyev, the outspoken dean of the New Economic School, has abruptly left Russia for France as concerns mount that Russia's best and brightest are being forced out of the country amid a crackdown on dissenters.

The father of a Chechen man shot dead by the FBI during questioning about his links to the Boston Marathon bombers said Thursday he wanted the agents tried for "executing" his son.

Ibragim Todashev, 27, was shot by FBI agents in Florida a week ago during questioning at his home about his links to one of the Tsarnaev brothers alleged to have carried out the April 15 Boston bombings.

Russia has delivered sophisticated air defense missiles to Syria, President Bashar Assad has implied in an interview to be aired Thursday on Hizbullah's al-Manar television, the network said.

Al-Manar said in a statement that when asked about the promised delivery of the S-300 surface-to-air missiles, Assad replied: "All the agreements with Russia will be honored and some already have been recently."