Washington ? Gen. Salim Idriss, the commander of rebel forces in Syria, complained late Tuesday that President Obama’s desire “to wait and wait for more evidence” that the Syrian regime has used chemical weapons is encouraging their continued use — and that these attacks will only stop if the U.S. and its allies impose a no-fly zone.

Idriss, who heads the moderate wing of the Free Syrian Army, has emerged as the key U.S. ally in the Syrian conflict. While he appreciates the recent increase in U.S. training and humanitarian support, and the talk in Washington of sending lethal aid, he was clearly frustrated by the comments that Obama had made to reporters a few hours earlier.

Obama said in the televised news conference that he wanted solid evidence of chemical weapons that could prompt international action against Bashar al-Assad. “If we end up rushing to judgment without hard, effective evidence, then we can find ourselves in a position where we can’t mobilize the international community to support what we do,” Obama said.

But Idriss countered that his forces have enough information now to answer Obama’s questions of how, where and when the weapons were deployed on four separate occasions. He welcomed U.S. plans to train his forces but said this strategy will be useless if Assad continues the chemical attacks. Idriss claimed the regime is delivering the chemical weapons with planes and Scud missiles, which he said must be destroyed.

Idriss, a German-trained engineer who defected from Assad last summer, voices moderate, nonsectarian views. He opposes the extremist al-Nusra Front and said he has ordered his fighters to stop cooperating with them. He repeated a February statement to me that he’s ready to negotiate a political transition with Syrian army commanders who haven’t ordered the deaths of civilians.

Idriss also offered to meet “right now” with Russian officials. “If they have some interests, we will discuss the Russian role in the future. We will be very positive,” he said.

The Obama administration sees Russia as a necessary participant in any negotiated political transition in Syria. Obama’s desire for Russian cooperation is one reason he has been cautious in responding to allegations that Assad has used chemical weapons. Obama talked by phone to President Vladimir Putin Monday, and an official said “we still do believe there’s a constructive role for Russia to play.”

Idriss was emphatic about his break from the al-Nusra Front, which is an offshoot of al-Qaida in Iraq. “We don’t work with al-Nusra. We don’t share anything with them.”

Building up Idriss’ Supreme Military Council is crucial given the administration’s expectation of a continuing struggle after Assad is toppled. “There could be a second war after Assad falls … as factions battle for control,” explained a senior administration official Tuesday. The official said the extremist threat had been discussed with Russia, Saudi Arabia, Qatar, Turkey and others.

The U.S. official agreed that there was “a growing reluctance” among Idriss’ mainstream umbrella group to work with al-Nusra, especially after it formally pledged allegiance to al-Qaida in Iraq a few weeks ago. “Al-Nusra’s gains haven’t been arrested, but their progress has been decelerated,” said the U.S. official.

Whether Idriss and his moderate forces can expand their command-and-control network is the crucial issue for the U.S. — and also the most problematic. The Syrian opposition is almost entirely Sunni Muslim and has deep Islamist roots. The battalions nominally under Idriss’ command have been fighting alongside jihadist groups for more than a year, and it will take more than official statements to accomplish a separation.

Squeezing the extremists will be impossible without more help from Turkey, across whose border the Syrian jihadist fighters travel daily to receive money and supplies from wealthy Gulf Arabs. The U.S. is hoping that Turkey will crack down harder on this cross-border traffic, and this will be a key topic when Turkish Prime Minister Recep Tayyip Erdogan visits Washington in mid-May.

To underline his plea for help, Idriss is sending a letter to Obama. “Mr. President, I understand the reasons behind your cautious involvement in Syria,” a draft said. “We desperately need your support, as the Free Syrian Army under my command has neither the requisite training nor equipment to counter the effects of Assad’s chemical weapons or to destroy them.”

Idriss told me he appreciated a big delivery of U.S. supplies Tuesday, marked with the logo of his Supreme Military Council. The shipment was mostly food.