Sen. Dianne Feinstein (D., Calif.) had dinner with Iranian Foreign Minister Javad Zarif, Politico reported Thursday.
Feinstein's office said her dinner was "arranged in consultation with the State Department."
The State Department said it had not asked the senior senator from California to attend the dinner.
Zarif has served in his post since 2013. He negotiated the Joint Congressional Plan of Action (JCPOA), the Iran nuclear agreement, with then-Secretary of State John Kerry. In February of this year, he announced he would be resigning from the post. After several days of confusion, the Iranian government clarified he would remain in his role.
Politico reported last week that Feinstein was seen holding an unlocked phone with Zarif's contact information open. At the time, her office declined to confirm her communication with the Persian diplomat.
This week, Zarif accused the United States of playing a "dangerous game" with its response to Iranian escalations. He has refused to negotiate with the White House to calm the situation unless the U.S. shows sufficient "respect" to the theocratic regime.
Tension between Iran and the United States has only heightened since President Donald Trump withdrew from the JCPOA last May. According to information released by the White House in March, Iran is responsible for some six hundred American fatalities in Iraq between 2003 and 2011.
U.S. assessment determined that Iran was behind attacks on two Saudi Arabian oil tankers and a Norwegian ship earlier this month. Satellite images found that Iran had loaded fully assembled missiles onto small ships, raising concerns that the Iranian Revolutionary Guard Corps (IRGC) was preparing to strike American or allied assets in the Persian Gulf.
The IRGC, a paramilitary group, responds directly to Supreme Leader Sayyid Ali Hosseini Khamenei, not to Iran's quasi-democratically elected government. The U.S. designated it a terror organization last month.
Trump responded to Iranian provocation with threats of force, insisting he was prepared to speak with the Iranians, but would not tolerate provocations.
On Sunday, he promised any fight would usher in "the official end of Iran."
In the days since, Iran has removed the missiles from the ships, prompting some U.S. officials to consider the situation improved.
Thursday, news organizations reported that the Pentagon was preparing contingency situations in which as many as 10,000 troops would head to the region to counter conventional Iranian efforts.