U.S. officials, meanwhile, directed reporters’ attention to the actions of the Syrian government. The State Department denounced pro-Assad forces’ use in recent weeks of so-called “barrel bombs,” highly inaccurate canisters loaded with explosives and shrapnel that are rolled out of the back of regime helicopters. Additionally, unnamed U.S. officials told The New York Times that the Assad regime had recently fired Soviet-era SCUD missiles into rebel-held territories in northern Syria. Neither the State Department nor Pentagon would confirm or deny that report, however, citing intelligence reasons, and there was no confirmation from inside Syria.

The United States is pursuing a strategy of isolating Nusra’s militant Islamists by labeling them terrorists and redirecting aid to political and military rebel factions that have signed on to plans to create a democratic, pluralistic Syria once Assad falls.

In Washington, State Department spokeswoman Victoria Nuland told reporters that Nusra’s terror designation was intended for two audiences: ordinary Syrians, on whom the U.S. is counting to isolate extremist rebel factions, and the United States’ “partners who have made choices other than ours in terms of the way they are supporting the opposition” – code for U.S. allies Saudi Arabia and Qatar, who’ve been providing weapons and money to Islamist rebel groups.

But the policy seems to be backfiring in Syria, where expressions of support for Nusra could be seen in demonstrations and on web forums where people were asked to sign statements proclaiming, “We are all Jabhat al Nusra,” as the group is called in Arabic.

“It has made them more popular,” said Ammar Dandash, a Syrian journalist from the northern province of Idlib. He said most Syrians who support the opposition are frustrated with the United States and its Western allies after more than a year when requests for arms had gone unheeded.

Nusra began carrying out secretive car and suicide bombings in late 2011, according to U.S. officials, when al Qaida in Iraq’s top leader, Abu Du’a, dispatched another al Qaida in Iraq leader to Syria to join in the anti-Assad rebellion. The State Department said Abu Du’a continues to advise Nusra on tactics and policy.

At first, many anti-Assad activists denied that the group was working with the rebels, claiming that the Syrian government had created it to discredit the opposition. Now, however, Nusra’s influence has surged over the rebellion, not only with bombings in Damascus and other cities, but in more traditional military operations where battalion-size Nusra units have been instrumental in insurgent successes across the country.

Many rebels said singling out Nusra as a terrorist organization might make the group more popular. They also said it was unfair to single out Nusra when other rebel groups share similar ideology. Ahrar al Sham, for example, is another group whose tactics include suicide bombings and whose fighters adhere to a literalist interpretation of Islamist doctrine.

“This declaration could also include other groups – it needs more explanation,” said Jawad Abou-Hatab, who belongs to the newly recognized Syrian coalition. “Jabhat al Nusra is defending its country.”

Abou-Hatab depicted Nusra’s presence as the healthy emergence of political plurality in the space wrested from the Assad dynasty’s four-decade authoritarian stranglehold. In the new Syria, he suggested, there would be room even for views that are anathema to the West.

“They have the right to their opinion,” he said of Nusra, “which is that an Islamic country is inclusive.”