WASHINGTON -- The United States and Germany yesterday warned Russia not to endanger a planned peace conference for Syria or alter the balance of power in the Middle East by providing an advanced air defense system to President Bashar Assad's embattled regime.

Secretary of State John Kerry and German Foreign Minister Guido Westerwelle said the transfer of S-300 missiles from Russia to Syria would prolong the country's civil war, imperil attempts to form a transitional government through negotiation and hurt Israel's strategic interests.

"It is not helpful to have the S-300 transferred to the region while we are trying to organize this peace [conference' and create peace," Kerry told reporters at a joint news conference with Westerwelle. "We ask them again not to upset the balance within the region with respect to Israel."

Westerwelle called on Russia not to "spoil" the peace conference, which was planned for Geneva this month but has been delayed until July at the earliest.

Russian officials have said they will supply the S-300s to Syria under an existing contract. They have also said that they will try to persuade the Assad regime to participate in the Geneva peace talks. But the Syrian opposition has said it will not attend the conference while massacres are continuing.

Kerry said he believed the opposition would attend once it straightens out questions about its leadership.

He also warned anew that the use of chemical weapons is a "red line" for the Obama administration. At the same time, he said evidence that such weapons have, in fact, been used, is still being vetted for 100 percent certainty.

"We are doing our due diligence, as we should do given past experience, to make certain that the intelligence is correct . . . and then make judgments that are appropriate," Kerry said. -- AP

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