The developments point to the delicate balance that the United States is trying to maintain. On the one hand, it is exploring a proposed deal that could create common ground with President Bashar al-Assad’s main supporters, Russia and Iran, and might eventually lead to a political settlement of the Syrian civil war. On the other hand, it is keeping up military pressure on Mr. Assad and trying to avoid alienating Saudi Arabia and other gulf allies that the United States has relied on to work with the rebels.

“My sense,” Mr. Hassan said, “is that the Americans are reassuring them behind the scenes.”

The situation points to the many competing interests the United States is trying to balance in the Syria crisis. The Americans’ stated goal in Syria is a political settlement, but that outcome is all but impossible to achieve without talking to Syria’s allies. And the close association among Saudi Arabia, Qatar and rebel groups has been a source of mistrust for government supporters inside Syria and others outside the country who fear the Islamic militants who have risen to prominence on the battlefield on the strength of financing from private donors in the gulf.

While Saudi Arabia has a strong interest in capitalizing on the Syrian crisis to weaken Iran and sever its alliance with Syria, the Saudis also fear the growing power of the many jihadists among the Syrian rebels. So far, analysts and rebels say, it has heeded American requests not to deliver antiaircraft missiles that could fall into the hands of Islamic militants who might use the missiles against other governments, not just Mr. Assad’s.

For months, Saudi Arabia has been quietly funneling arms, including antitank missiles, to Free Syrian Army groups through Jordan, working covertly with American and British intelligence and Arab governments that do not want their support publicly known, according to rebel groups operating in southern Syria.

Ahmed Abu Rishan, a spokesman for a special forces group that belongs to General Idris’s general command in southern Syria, said Thursday that those deliveries had increased in recent days.

The weapons helped rebel groups take over a tank battalion and destroy four tanks in the village of Sheikh Saad near the southern border, he said, providing a video of the attack that appeared to demonstrate the use of antitank guided missiles.