Serious ambiguities dwell with the real intention of an emerging US-led coalition to fight Islamic State (IS) militants in Iraq and Syria, Iran's Foreign Ministry spokeswoman Marzieh Afkham said here on Thursday.

"There are doubts about the seriousness of the coalition which has come to existence after the (recent) NATO summit in its fight against terrorists," Afkham was quoted as saying by official IRNA news agency.

The Iranian spokeswoman criticized what she called the "West's double standards" toward terrorism and extremism, saying that the West's treatment of terrorism will bear "no result but the spread of terrorism and extremism as well as emergence of their new branches in different parts of the world."

One month after launching airstrikes against Islamic State militants in Iraq, US President Barack Obama on Wednesday vowed that he "will not hesitate to take action" against the IS in Syria and Iraq.

Obama said Washington will work with its friends and allies to "degrade and ultimately destroy" IS forces, which poses a threat to the people of Iraq and Syria, and the broader Middle East, including American citizens, personnel and facilities.

He noted that the United States will lead a broad coalition to roll back this terrorist threat and use airpower to take out IS forces "wherever they exist."

Afkham said certain members of the so-called coalition are among financial and security supporters of the terrorists in Iraq and Syria and some others have failed to act according to their international responsibility regarding Iraq and Syria.