On Monday, US President Barack Obama said US special forces had already started to support local groups on the ground in Syria in their fight against the Islamic State (ISIL, or Daesh in Arabic) jihadist group.
"Sending troops to Syria by any state to fight ISIL or to train local forces to fight ISIL without the consent of the Syrian government is a serious violation of the UN Charter and international law that prescribe the principle of respect for state sovereignty," Jaafari said, commenting on Obama's statement.
Jaafari added that Syria continued to fight terrorism on its territory in adherence to the state's constitutional obligations and the principles of international law, the UN Charter and UN Security Council resolutions.
In October, Washington announced it would send some 50 US special forces members to Syria to assist so-called moderate opposition factions to fight Daesh jihadists.
US Secretary of Defense Ashton Carter said earlier in December that the United States would be looking for opportunities to send additional special operations forces to Syria to assist the fight against Daesh.
A US-led international coalition has been conducting airstrikes against Daesh, which is prohibited in Russia and many other countries, in Iraq and Syria since 2014 without the approval of the UN Security Council or the Syrian government. Russia launched its own air campaign against Daesh in Syria on September 30, at the request of Damascus.