WASHINGTON -- Intelligence suggests the Syrian government has moved some of its chemical weapons in order to protect them, but the U.S. believes that the main sites remain secure, Defense Secretary Leon Panetta said Friday, indicating there are lingering questions about what exactly happened to some of the weapons.

It was the first time Panetta confirmed that U.S. officials believe there have been multiple "limited" movements of the chemical weapons, but he said Syrian officials were relocating them in order to better secure them.

"There has been intelligence that there have been some moves that have taken place. Where exactly that's taken place, we don't know," Panetta told reporters. "I don't have any specific information about the opposition and whether or not they've obtained some of this or how much they've obtained and just exactly what's taken place."

Asked specifically if there was any belief that the Iran's powerful Revolutionary Guard or the rebel forces have been able to get possession of any of the weapons, Panetta appeared to leave the door open to that possibility, saying he has no "firm information to confirm that that's taken place."

He said the U.S. has monitored the main sites and determined that they are still secure.

There have been ongoing concerns that the opposition forces battling the regime of Syrian President Bashar Assad or other militant forces in the country may get their hands on the weapons caches.

It is widely believed that Syria possesses extensive chemical and biological weapons stockpiles and it has threated to use them if the country comes under attack.

President Barack Obama has declared that the threat of chemical or biological warfare in Syria is a "red line" for the U.S., and has warned that the U.S. will not tolerate it if the weapons fall into the wrong hands. He said there would be enormous consequences if the U.S. sees any movement or use of the weapons.

Panetta was speaking at a news conference with Canadian Minister of National Defense Peter MacKay.

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  • In this Friday, Sept. 21, 2012, photo, a Syrian shouts slogans against the regime in front of a flag of the armed Islamic opposition group, the Nusra front, during a demonstration in the Bustan al-Qasr neighborhood of Aleppo, Syria. Arabic from the Quran reads, "There is not God but Allah, and Muhammad is his messenger." (AP Photo/ Manu Brabo)

  • In this Friday, Sept. 21, 2012, photo, a Syrian man looks at his mobile phone in the Bustan al-Qasr neighborhood of Aleppo, Syria. The Britain-based Syrian Observatory for Human Rights said Friday that nearly 30,000 Syrians have been killed during the 18-month uprising against the Assad regime. (AP Photo/ Manu Brabo)

  • In this Saturday Sept. 22, 2012, photo, a Free Syrian Army soldier stands next to a dead body in front of Dar el-Shifa hospital in Aleppo, Syria. Partial translation in Arabic reads, "Free Syrian Army." (AP Photo/ Manu Brabo)

  • In this Sunday, Sept. 23, 2012, photo, Syrian children laugh on a truck, as they flee with their family, due to fighting between Syrian rebels and government forces, in Aleppo, Syria. (AP Photo/ Manu Brabo)

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  • In this Thursday, Sept. 20, 2012, file photo, a wounded woman, still in shock, leaves Dar El Shifa hospital in Aleppo, Syria. Two months into the battle for Syria's largest city, civilians are still bearing the brunt of the daily assaults of helicopter gunships, roaring jets and troops fighting in the streets. (AP Photo/ Manu Brabo, File)

  • Free Syrian Army fighter takes a rest in a hole on a building during an attack on Syrian Army positions in Aleppo, Syria, Tuesday, Sept. 25, 2012. (AP Photo/Manu Brabo)

  • A Syrian woman cries near Dar El Shifa hospital while the body of her son, killed by the Syrian Army, lies on the street in Aleppo, Syria, Tuesday, Sept. 25, 2012. (AP Photo/Manu Brabo)

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  • A Free Syrian Army fighter holds a rocket-propelled grenade launcher while taking cover after a tank blast in Aleppo, Syria, Wednesday, Sept. 26, 2012. (AP Photo/Manu Brabo)