This story was updated at 12:59 p.m. ET

The U.S. government has suspended all non-lethal aid to the Western-backed military wing of the Syrian opposition.

The suspension, which was announced Wednesday, began on the weekend after Islamist rebel groups seized control of warehouses containing communications equipment and other aid items.

NPR's Deborah Amos, who is in Beirut, filed this story for our Newscast unit:

"The U.S. has cut off the Supreme Military Council indefinitely, according to a U.S. Embassy spokesman in Turkey. The SMC is the Western-backed rebel group, also known as the Free Syrian Army.

"Late Friday, the Islamic Front, a union of six major rebel groups, seized an SMC complex close to the Turkish border, capturing the headquarters and warehouses where the non-lethal aid was stored. U.S. government sources told NPR that the seized equipment included pickup trucks, packaged meals and radio gear.

"U.S.-funded humanitarian aid will continue into northern Syria, according to U.S. officials."

The Islamic Front says its goal is to set up an Islamic state in Syria.

As Deb reported in September, "moderate rebel groups in Syria are becoming less influential in comparison to more radical Islamist factions."

"The civilian, secular democracy folks have been sidelined," David Kilcullen, the CEO of Caerus, a Virginia-based strategy firm, told Deb. "That is just a fact of life, and I do think it's tragic. Today, you are looking at a polarized resistance, a larger number at the extremes."

Reuters, meanwhile, reported that Britain also is suspending non-lethal aid to the rebels.

The SMC called the decisions mistaken.

"We hope our friends will rethink and wait for a few days when things will be clearer," spokesman Louay Meqdad said, according to Reuters.

In London, Prime Minister David Cameron emphasized the need to work with moderate members of the Syrian opposition. "We must not allow this argument to develop that the only opposition in Syria is an extremist opposition," he told lawmakers.

The opposition infighting comes amid gains by Assad's regime in the fighting that has gripped the country. And as Deb reported last month:

"The regime is unlikely to retake all rebel-held areas, says [military analyst Jeffrey] White. But recent gains show the momentum has shifted. Is the Syrian army stronger, or the rebels weaker? Analysts say it's a bit of both. Mainstream rebel groups backed by the West and Saudi Arabia have been weakened by infighting, challenged by radical Islamist brigades, some of them tied to al-Qaida."

The nearly three-year civil war has killed more than 100,000 people and created a massive refugee crisis that has affected Syria's neighbors.

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