The comments by the head of the Free Syrian Army came as President Bashar Assad told Russian state television his government agreed to surrender its chemical weapons in response to Russia's initiative and not because of a threatened U.S. attack.
Gen. Salim Idris' statement was broadcast on pan-Arab satellite channels hours before talks in Geneva between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov on the Russian proposal.
"We call upon the international community, not only to withdraw the chemical weapons, that were the tool of the crime, but to hold accountable those who committed the crime in front of the International Criminal Court," Idris said.
He added that the FSA "categorically rejects the Russian initiative" as falling short of the expectations of rebel fighters.
The U.S. accuses Assad's government of being behind the Aug. 21 attack in the suburb of Ghouta, which the U.S. says killed 1,429 people. Other estimates of the deaths are lower.
Assad has denied responsibility and accuses U.S. officials of spreading lies without providing evidence.
The Russian proposal has, at least for the moment, averted the threat of U.S. military action against Syria. Many rebels had held out hopes that U.S.-led punitive strikes on Assad's forces would help tip the scales in their favor in Syria's civil war, which has claimed over 100,000 lives so far.
In an interview set to be broadcast Thursday, Assad told Russia's state Rossiya 24 news that "Syria is transferring chemical weapons under international control because of Russia."
Assad added that "the U.S. threats hadn't influenced" his government's decision.
Syria's Deputy Prime Minister Qadri Jamil suggested on Thursday that the Russian proposal will only succeed if the United States and its allies pledge not to attack Syria in the future.
"We want a pledge that neither it (the U.S.) nor anyone else will launch an aggression against Syria," Jamil told The Associated Press in Damascus. He did not elaborate. Jamil was responding to a question on his expectations from the meeting Thursday between Kerry and Lavrov.
Kerry and a team of U.S. experts will have at least two days of meetings with their Russian counterparts in Geneva. They hope to emerge with an outline of how some 1,000 tons of chemical weapons stocks and precursor materials as well as potential delivery systems can be safely inventoried and isolated under international control in an active war zone and then destroyed.
Officials with Kerry said they would be looking for a rapid agreement on principles for the process with Russians, including a demand for a speedy Syrian accounting of their stockpiles.
The agency also has arranged for the Syrian opposition to receive anti-tank weapons like rocket-propelled grenades through a third party, presumably one of the Gulf countries that has been arming the rebels, a senior U.S. intelligence official and two former intelligence officials said Thursday. They spoke on condition of anonymity because they were not authorized to discuss the classified program publicly.
Loay al-Mikdad, a Free Syrian Army spokesman, told the AP that they have not received any weapons from the U.S. although they expect that in the near future.
Meanwhile, the Syrian Observatory for Human Rights said rebels fighting Assad's forces captured Thursday the village of Imm al-Lokas in the southern region of Quneitra near Syria's Israeli-occupied Golan Heights.
The Britain-based activist group added that rebels also captured several army posts in the area in heavy fighting that caused casualties on both sides.
It also said that in the northeastern province of Hassakeh, clashes between Kurdish fighters and members of the al-Qaida-linked Nusra Front and the Islamic State in Iraq and the Levant in the past two days killed 13 Kurdish gunmen and 35 militants.
The two sides have been fighting in northern Syria for months in clashes that left scores of people dead on both sides.
Syrian state media said government troops advanced in the predominantly Christian village of Maaloula near Damascus, capturing the main square as well as the Mar Takla convent where several nuns were staying.
A resident in the village told the AP that troops were trying to capture a rebel-held hotel on a hill overlooking the area. The man, who spoke on condition of anonymity for fear of reprisals, said most of the fighting Thursday was taking place in the western part of the village.
Government troops are trying to flush out rebel units, including two linked to al-Qaida, from the hilltop enclave the rebels broke into last week.
Most of the village's 3,300 residents have fled to safer parts of the country, although some have remained, hunkering down in their homes, activists said.
Maaloula, about 60 kilometers (40 miles) northeast of Damascus, had until recently been firmly in the regime's grip despite being surrounded by rebel-held territory. The village was a major tourist attraction before the civil war. Some of its residents still speak a version of Aramaic, a biblical language believed to have been used by Jesus.