United States intelligence agencies have detected no new moves by the Syrian government in recent days that would indicate it was preparing to use chemical weapons against rebel forces, US Defense Secretary Leon Panetta said on Tuesday.
Several Western countries issued coordinated warnings last week to President Bashar Assad not to deploy chemical weapons, many citing secret intelligence that US officials have said his government might be preparing to use poison gas.
Syria has rejected the warnings as "a pretext for intervention" by outsiders.
"At this point, the intelligence has really kind of leveled off. We haven't seen anything new indicating any aggressive steps to move forward in that way," Panetta said, speaking to reporters before arriving on a visit to Kuwait.
Panetta was outspoken about his concerns last week that Assad's government was considering using chemical weapons as rebels intensified their push, particularly on Damascus.
He said on Tuesday he still held those concerns.
"I'd like to believe he's got the message. We've made it pretty clear and others have as well," he said.
"But it's also clear that the opposition continues to make gains in Syria and our concern is that if they feel like the regime is threatened with collapse that they might resort to these kinds of weapons," he said.
US President Barack Obama has warned of consequences should Assad use the weapons. Panetta said the United States was monitoring the situation very closely.
Panetta said his visit to Kuwait was mainly to visit the more than 13,500 US troops in the country before the Christmas holiday. He also planned to meet Kuwaiti leaders.
US blacklists radical Islamist Syrian rebel group
The United States has designated the radical Islamist Syrian rebel group Jabhat al-Nusra, which is suspected of ties to al-Qaida, as a foreign terrorist organization.
In an order released on Tuesday, the US State Department essentially classified the group, which has advocated for an Islamic state in Syria, as an affiliate of al-Qaida in Iraq.
By blacklisting al-Nusra, authorities now can freeze any assets the group or its members have in US jurisdictions. The designation also prohibits Americans from giving it any material support.
The group has been accused by other rebel factions of indiscriminate tactics in the bloody civil war aimed at ousting Assad.
"The secretary of state concludes that there is a sufficient factual basis to find that al-Qaida in Iraq ... uses or has used additional aliases," including Jabhat al-Nusra, the State Department statement said.
Tuesday's action comes as US officials attend the Friends of Syria meeting in Marrakesh, Morocco, to discuss the 20-month-old crisis in Syria as rebels push forward on the battlefield and move to unify the political opposition.
US officials have stressed their concern about the rising influence of extremist elements in the Syrian war.
Secretary of State Hillary Clinton had been expected to attend before falling ill with a stomach virus. Deputy Secretary of State Bill Burns is attending in her place.