"The United States condemns any terrorist attack anywhere, period. We've always stood by that," Nikki Haley, the US ambassador to the United Nations, told CNN.
Iranian lawmakers launched impeachment proceedings against the education minister on Wednesday, stepping up pressure on President Hassan Rouhani
Masoud Karbasian lost the vote of confidence, which was carried live on state radio, by 137 votes to 121.
Iran's President Hassan Rouhani said on Monday that Washington's call for new nuclear negotiations at the same time the US reimposes crippling sanctions "makes no sense".
Iran faces increased US pressure and looming sanctions after Trump's decision to withdraw the United States from a 2015 international deal over Iran's nuclear programme.
Donald Trump says that unless European allies rectify "flaws" in Tehran's deal with world powers by May 12 he will refuse to extend US sanctions relief for Iran.
Hassan Rouhani said before leaving Iran that foreign forces operating in Syria without approval from the Damascus government should leave.
The review of US nuclear policy published on Friday has riled Russia, which viewed the document as confrontational, and raised fears that it could increase the risk of miscalculation between the two world powers.
British Foreign Secretary Boris Johnson met Iranian President Hassan Rouhani for nearly an hour on Sunday in his attempt to secure the release of British-Iranian Nazanin Zaghari Ratcliffe.
The Iranian parliament voted on Sunday to keep the oil and foreign ministers, two of pragmatist President Hassan Rouhani's key members of cabinet, in their posts.