Are Syrian weapons flooding into Lebanon? That's the chatter in national-security circles this week, leading some in Congress to raise concerns over the Obama administration's decision to send a U.S. envoy back to Damascus after a long period of downgraded relations.

Informed administration sources said they were well aware of the rumors that unspecified amounts of a new type of weaponry are making their way over the border and into Hezbollah hands. Sources close to the issue said that the weapons were of a characteristic and range that could pose a risk to large swaths of Israel, not just the communities in the north that already live every day under the threat of short-range rocket attacks.

There have been scattered, unverified reports since late last year that Syria was moving some of its arsenal of Scud missiles toward Lebanon, but few if any in the Western press. Syria is thought to have several hundred of the Soviet-era Scuds and other short-range ballistic missiles in its arsenal.

Now, the rumors that the weapons have moved into Hezbollah hands are raising tensions in the region and heightening concern here in Washington.

One Middle East insider told The Cable that the concern is coming primarily from Capitol Hill. "There is serious concern in Congress about just how bad Syria's behavior has been lately, from their flagrant ties with terrorist groups and Iran, to deeply worrying arms shipments to Hezbollah in Lebanon."

A Senate leadership aide confirms that there is now at least one hold on the nomination of Robert Ford to become the first U.S. ambassador to Syria in more than four years. Some congressional sources said there were multiple holds. The lawmakers are said to be pressing for more intelligence-sharing on the Syrian weapons transfers as part of their demands before considering Ford. (Other reasons why senators are holding up the Ford nomination can be found here.)

The administration sources we spoke with they had no clear understanding about exactly what the current state of play was regarding the weapons. That has led some to privately wonder why the situation wasn't being more closely tracked, although that may very well be going on at levels we can't see.

National Security Spokesman Mike Hammer told The Cable that the administration is "increasingly concerned about the sophistication of the weaponry being transferred and have continued to reiterate our strong concerns to the Syrian and Lebanese authorities."

"The transfer of weapons from Syria to Lebanese Hizballah undermines the Lebanese government's ability to exercise sovereignty over all of its territory and risks sparking a conflict that no one needs," he added.

Several senators have been traveling in the region, including in Syria, during their legislative recess. Sources contacted who are on those delegations refused to comment on the rumors in any way, citing the extreme sensitivity of the issue.

Senate Foreign Relations Committee chairman John Kerry strongly expressed his concerns about Syrian weapons flows into Lebanon when visiting Damascus last week. "That is something that must stop in order to promote regional stability and security," Kerry said.

But Ahmed Salkini, a spokesman for the Syrian Embassy in Washington, strongly denied the allegations.

"These reports are unequivocally false and are a product of the Israeli government that is trying to speciously create a raised level of tension in the region to justify a future conflagration of violence on their part, or simply to divert attention from the real issue at hand: Israeli settlements and expansionism," he told The Cable.