In an interview from his office in Damascus on Friday, Assad said he supported peace talks, but that negotiations do "not mean that we stop fighting terrorism".
He said a major Russian-backed government offensive under way in the northern province of Aleppo was aimed mainly at severing the opposition's supply route from Turkey.
Assad said he saw a risk that Turkey and Saudi Arabia, key backers of the opposition, would intervene militarily in Syria.
He also addressed the massive flow of refugees from his country, saying it was up to Europe to stop "giving cover to terrorists" so that Syrians could return home.
Assad rejected UN allegations of regime war crimes, describing them as "politicised" and lacking evidence.
With air support from key ally Russia and backing by pro-government fighters, regime troops have nearly encircled Aleppo, Syria's second city.
Assad said his regime's eventual goal was to retake all of Syria, large swathes of which are under the control of rebel forces or the Islamic State jihadist group. "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," he added. Assad 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.