The State Department warned Monday that Americans traveling to Iran run a risk of being arrested and detained, in a notice that updated its prior warning about Iran travel from mid-March.

"U.S. citizens traveling to Iran should very carefully weigh the risks of travel and consider postponing their travel," the department said. "U.S. citizens residing in Iran should closely follow media reports, monitor local conditions, and evaluate the risks of remaining in the country."

"The U.S. government's ability to assist U.S. citizens in Iran in the event of an emergency is extremely limited," it said. "U.S. citizens in Iran should ensure that they have updated documentation at all times and make their own plans in the event of an emergency."

The warning was renewed after the Obama administration spent the day defending the Iran nuclear agreement and a $1.7 billion payment it made to the country to compensate the country for a botched arms deal decades earlier.

"Iranian authorities continue to unjustly detain and imprison U.S. citizens, particularly Iranian-Americans, including students, journalists, business travelers, and academics, on charges including espionage and posing a threat to national security," it said. "Iranian authorities have also prevented the departure, in some cases for months, of a number of Iranian-American citizens who traveled to Iran for personal or professional reasons."

State noted that the U.S. government has no diplomatic relations with Iran, and therefore can't protection for people there. It also said Iran doesn't recognize dual citizenship, and won't allow the Swiss to protect those with dual status.

It also warned that people of non-Muslim faith could be in trouble there.

"The Iranian government continues to repress some minority religious and ethnic groups, including Christians, Baha'i, Arabs, Kurds, Azeris, and other," it said.