By MATTHEW LEE, AP Diplomatic Writer

WASHINGTON (AP) — The Obama administration is weighing an offer from Russia to have military-to-military talks and meetings on the situation in Syria amid increasing U.S. concern and uncertainty about Russia's military buildup there, Secretary of State John Kerry said Wednesday.

Kerry said Russian Foreign Minister Sergey Lavrov had proposed the consultation in a phone call on Tuesday and that the White House, Pentagon and State Department were considering it. Kerry suggested that he favored such an idea, noting that the United States wants a clear picture of what Russia's intentions are in Syria following a recent military buildup there.

Lavrov proposed a "military-to-military conversation and meeting in order to discuss the issue of precisely what will be done to deconflict with respect to any potential risks that might be run and have a complete and clear understanding as to the road ahead and what the intentions are," Kerry told reporters at a joint State Department news conference with South Africa's foreign minister.

"You have a conversation in order to do that," Kerry said. "It is vital to avoid misunderstandings, miscalculations (and) not to put ourselves in a predicament where we are supposing something and the supposition is wrong."

Kerry said Lavrov had told him that Russia was only interested in confronting the threat posed by the Islamic State group in Syria. But Kerry stressed it remained unclear if that position would change and Russia would mount a defense of Syrian President Bashar Assad who the U.S. believes must leave power.

"Obviously, there a questions about that," he said. "I am not taking that at face value."

However, he added that if Russia is only focused on the Islamic State group then it remains a potential partner in pushing for a political transition in Syria. "If Russia is only focused only on ISIL and if there is a capacity for cooperation ... there still is a way to get a political negotiation and outcome," he said.

Kerry also said he had spoken on Wednesday with Israeli Prime Minister Benjamin Netanyahu who office announced earlier that he would visit Moscow next week to discuss Syria with Russian President Vladimir Putin.

His comment come as Russia's military buildup in Syria has perplexed the Obama administration and left it in a quandary as to how to respond.

In his call with Lavrov on Tuesday, his third in 10 days, Kerry said he sought clarity about Moscow's moves and warned that Russian support for Assad "risks exacerbating and extending the conflict."

In the afterglow of the Iran nuclear deal, which was hailed by the Obama administration as the kind of diplomacy that can be achieved when Russia and the United States cooperate, U.S. officials had hoped for a change in Russia's position about Syria, potentially even enlisting its support to move Assad out.

Moscow's latest actions, however, have taken many by surprise and further muddied efforts to fight Islamic State militants while trying to promote political transition in Syria.

In recent days Russia has sent about a half-dozen battle tanks and other weaponry — along with military advisers, technicians, security guards and portable housing units — to Syria with the apparent goal of setting up an air base near the coastal town of Latakia, a stronghold of the Syrian president.

U.S. officials say Putin's intentions in Syria, particularly in the medium- to long-term, remain a mystery.

"The decision-making process in that country is rather opaque," White House spokesman Josh Earnest said of Russia, adding that Moscow has long used Syria as a "client state."