The United States and Germany are urging Russia not to provide the regime of Syrian President Bashar al-Assad with advanced anti-aircraft missiles.
After talks Friday in Washington, U.S. Secretary of State John Kerry and German Foreign Minister Guido Westerwelle said any Russian arms supplies to Syria could prolong the country's civil war.
Kerry also said a Russian transfer of the S-300 air defense system to Syria would put Israel's security at risk.
"It is not helpful to have the S-300 transferred to the region while you are trying to organize this peace and create peace. 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," said Kerry.
Westerwelle called weapons deliveries to the Assad regime "totally wrong." He also said the transfers may hurt chances of getting the Syrian government and the opposition into peace talks that were tentatively planned for Geneva next month.
"It is very important that this Geneva conference gets a realistic chance and, therefore, we ask and we urge everyone not to spoil this conference. Both parties have to participate, and everyone in the international community should understand how important this conference is, and this is perhaps a window of opportunity. No one knows if this conference will become a success. But I think it is the wrong message which has been sent by our colleagues in Russia to the world and to the region by delivering S-300 or other parts of weapons," said Westerwelle.
Russia has vowed to proceed with the transfer of anti-aircraft missiles to help deter foreign involvement in Syria's civil war. But on Friday, the Interfax news agency reported that delivery of the air-defense system to Syria may be delayed by several months. The Russian news agency quoted an arms industry source as saying the missiles would be transferred to Syria no earlier than September.
Israel has threatened to use force to stop the arms shipment. Earlier this month, Israel attacked a suspected weapons supply in Damascus in the belief the weapons were on the way to the Lebanese militant group Hezbollah.
Meanwhile, Syrian troops and their Hezbollah allies have come closer to capturing the town of Qusair, which controls supply routes vital to both sides in the Syrian war.
Local media reported troops have cut off rebel forces' supply routes in the Arjun district in northern Qusair. Pro-Assad forces have been surrounding Qusair in recent days.
Also, a U.S. citizen was killed in Syria while fighting for opposition forces. Syrian state media reported the woman, Nicole Mansfield, died during fighting in the town of Idlib. The U.S. Federal Bureau of Investigation confirmed the death to Mansfield's family.
In other news, the U.N. refugee agency said the number of Syrian refugees in neighboring countries passed 1.6 million this week.