The US has said the Syrian president is 'deluded' if he believes there is a military solution to the major conflict in his country.
It comes after Bashar al-Assad vowed to retake the country.
The Syrian leader's comments came after it was revealed a truce has been agreed for a "nationwide cessation" of violence in a week's time.
However, it is feared that the break in fighting will not hold.
The president raised concerns during an interview with news agency AFP, saying he backs peace talks but that negotiations do "not mean that we stop fighting terrorism".
Reuters reports that State Department spokesman Mark Toner said the president is "deluded if he thinks that there is a military solution to the conflict in Syria".
The White House has said the planned cessation of hostilities is an 'important step', but is calling for 'actions, not words' to illustrate the commitment.
Tens of thousands are continuing to flee Syria amid the fighting, which has resulted in the deaths of more than 260,000 people since 2011.
Director of Medicines San Frontiers Ireland Jane Anne McKenna says the comments from the country's president are concerning:
Syria's civil war has been raging since 2011, but the conflict entered a new phase last year when Russia started providing air support to government forces.
Aided by Russian air power, regime troops have nearly encircled Aleppo, Syria's second city.
Mr Assad said his eventual goal was to take back all of Syria, large parts of which are under control of rebel forces or IS.
"Regardless of whether we can do that or not, this is a goal we are seeking to achieve without any hesitation," he said.
"It makes no sense for us to say that we will give up any part," Mr Assad added.
He said it would be possible to "put an end to this problem in less than a year" if opposition supply routes from Turkey, Jordan and Iraq were cut.
But, if not, he said, "the solution will take a long time and will incur a heavy price".
Mr Assad's interview is the first he has given since the effective collapse of peace talks in Geneva earlier this month.
The talks have been "paused" until 25 February, and the truce is intended to bolster efforts for new negotiations.
