The US has been attempting to convince a key Syrian opposition group to agree to attend peace talks scheduled for next month, AFP cited a US official as saying Tuesday.
According to the official, the participation of the Syrian National Council was essential to the talks.
The biggest coalition within the opposition umbrella group over the weekend said it would not attend the peace forum and would quit the Syrian rebel bloc if it did, according to AFP.
"There have been many ups and downs in this process. And that's not unexpected given how challenging the situation is on the ground," AFP quoted US State Department spokeswoman Jen Psaki as saying.
"But we continue to press for the opposition to have a representative body at the Geneva conference," she added.