Russia and Iran are continuing to send arms to the Syrian regime that can be used against protesters, a top State Department official said today.

"Iran is resupplying Syria and through Syria has supplied weapons to Hezbollah," said Tom Countryman, the assistant secretary of state for international security and nonproliferation, at a Wednesday morning breakfast meeting of the Defense Writers Group in Washington.

Countryman's bureau plays a major role in monitoring international compliance with nonproliferation and arms control rules. He declined to go into specifics on what arms Iran and Russia are giving the regime of Bashar al-Assad, but he confirmed that both countries are still supplying arms that can be used to attack civilians and opposition groups inside Syria, who are engaged in an increasingly bloody struggle with the government.

"We do not believe that Russian shipments of weapons to Syria are in the interests of Russia or Syria," he said.

According to Countryman, the Iranian weapons being funneled through the Syrian government to Hezbollah are not being used by Hezbollah inside Syria, but are being transferred to Hezbollah groups inside Syria's neighbor Lebanon.

Countryman also said the U.S. government is working with allies to try to get a handle on the stores of conventional, biological, and chemical weapons inside Syria, to prevent them from falling into the wrong hands if and when the Assad regime collapses.

There are "tens of thousands" of MANPADS - shoulder-fired missile systems -- in Syria and nobody really knows where they all are, Countryman said. Unlike Libya, Syria is not a signatory to the Chemical Weapons Convention, so there is no official reporting on its store of those weapons, but the effort to locate them is underway.

"We have ideas as to the quantity and we have ideas as to where they are," Countryman said. "We wish some of the neighbors of Syria to be on the lookout... When you get a change of regime in Syria, it matters what are the conditions -- chaotic or orderly."

He also commented on the news that Iran has sent a letter to EU High Representative Catherine Ashton proposing a new round of nuclear talks between Iran and the P5+1 countries, a letter that Ashton has already said does not contain enough new concessions to justify a new meeting.

"This would be a good day for [Iran] to answer a letter sent four months ago," Countryman said, but what Iran really needs to do is open up fully to IAEA inspectors and directly address all of the questions about its nuclear program.

"There is a path forward where Iran can pursue peaceful use of nuclear energy," he said.

Former National Security Council Senior Director Dennis Ross argued in a New York Times op-ed today that the window for diplomacy with Iran is now open again because of the pressure wrought on Iran by international sanctions.

"The Obama administration has now created a situation in which diplomacy has a chance to succeed," wrote Ross. "It remains an open question whether it will."