Iran’s Supreme Leader Ayatollah Ali Khamenei advised Iranian politicians not to negotiate with the U.S. and rejected attempts by President Obama to start talks, referring to Obama’s outreach to himself and other leaders, the Washington Post reports.

Khamenei asked to be cautious and skeptical in dealing with the U.S. and criticized Obama for not altering U.S. policies toward Iran, arguing that the U.S. says it is willing to negotiate while threatening Iran with new sanctions.

In his harshest comments yet on the Obama administration, Khamenei said in a speech Tuesday that the United States has ill intentions toward Iran and is not to be trusted.

Khamenei said he had responded in March to Obama’s overtures, referring to a speech in which he said he would wait for changes in U.S. policy toward Iran before reassessing ties.

Since then, Khamenei said, “what we have witnessed is completely the opposite of what they have been saying and claiming. On the face of things, they say, ‘Let’s negotiate.’ But alongside this, they threaten us and say that if these negotiations do not achieve a desirable result, they will do this and that.”

Khamenei’s comments came as the U.S. and other world powers are still waiting for Iran’s answer to the nuclear fuel deal drafted in Vienna. After Tehran said last week it will seek changes to the plan, State Secretary Hillary Rodham Clinton said on Tuesday that it would not be altered, and that Iran should accept it as it is. 

Photo AFP/Getty Images/Behrouz Mehri via Time