German Foreign Minister Guido Westerwelle and US Secretary of State John Kerry say Syria's war may be prolonged if Russia provides the Assad regime with advanced air weapons. They say peace talks could also be at risk.
The pair met in Washington on Friday, ahead of peace talks scheduled for July that would attempt to bring Syria's warring parties together.
The talks between Westerwelle and Kerry came a day after claims from Syrian President Bashar al-Assad that his regime received a first shipment of the sophisticated S-300 anti-aircraft system.
At a joint news conference with Kerry, Westerwelle said Russia must not "endanger" the peace talks, and said plans to send the S-300s to Assad could also put Israel's security at risk. He called on Assad to "stop the violence and come to the negotiating table."
Kerry told reporters the weapons deliveries did not help the situation. Russia says they are being transferred under an existing contract.
"We ask them again not to upset the balance within the region with respect to Israel," he said. "The weaponry that is being provided Assad whether it is an old contract or not, has a profoundly negative impact on the balance of interests and the stability of the region and it does put Israel at risk."
On Tuesday, Russian Deputy Foreign Minister Sergei Ryabkov defended his country's decision to provide the system to the Assad regime, which came a day after the EU lifted its arms embargo against rebel groups. Ryabkov said it could deter Western nations from intervening in Syria's war.
The US has said it supports the EU's decision, but the Obama administration is against sending US weapons to rebels.
At least 80,000 people have died in the Syrian civil war, according to UN figures. Several million people have been displaced within Syria and over 1 million more into neighboring countries.
Kerry and Westerwelle also discussed Iran's nuclear program. Kerry said international patience was waning over what Iran asserts is a program meant for peaceful purposes.
"Every month that goes by gets more dangerous," said Kerry. He said he did not have high expectations that the upcoming presidential election in Iran would change the program, and repeated that it was unacceptable for Iran to have a nuclear weapon.
Westerwelle told the news conference that more diplomatic talks were necessary.
jr/mz (Reuters, AP)