"We tell our people in Syria that our war against the Syrian troops will not stop and no one can stop it," the group said in a statement.
The statement apparently came against the backdrop of the recent efforts by de Mistura, who proposed "frozen zones" in Aleppo province in order to establish a ceasefire that could later be replicated in other parts of the country.
Many rebel groups refused the initiative, but the Syrian government said that it was "worth studying," and that it was waiting for further details of a final say from de Mistura, mainly the results of the envoy's tour in the countries that have influence on the armed rebels in Syria.
The statement of the Nusra fighters is a clear indicator that the group would be another snag in the face of achieving pacification in the war-torn country.
The Syrian government has for long urged the international community to pressure countries that support the terrorist groups in Syria to stop doing so.
The Nusra Front, locally known as Jabhat al-Nusra, is a branch of Al Qaeda operating in Syria and Lebanon.
The group announced its formation Jan 23, 2012, during the Syrian Civil War.
It has been designated as a terrorist organisation by the UN, US, Australia, Canada, New Zealand, Saudi Arabia, Britain and Turkey.