Iran closed its borders Iraq and urged its citizens to avoid travel to the country, a senior official said amid an outbreak of violence after influential Shiite cleric Muqtada al-Sadr announced he was leaving politics.

At least 20 people were killed in violent clashes in the Iraqi capital Baghdad on Monday, when Sadr’s supporters stormed a government building and clashed with opposing factions after Sadr’s announcement.

Millions of Iranians visit the Iraqi city of Karbala every year for the Arbain religious holiday, which marks the end of 40 days of mourning for the Prophet Muhammad’s grandson, Imam Hussein. This year, Arbain falls on September 16-17.

“The border with Iraq was closed. For security reasons, Iranians should avoid traveling to Iraq until further notice,” Deputy Interior Minister Majid Mirahmadi was quoted as saying by state television.

State television said Iran had suspended all flights to Iraq until further notice due to ongoing unrest.

“We are trying to arrange an emergency flight to bring back Iranians from Iraq and Baghdad who are currently at the airport. We hope to remove them today,” state television quoted a senior civil aviation official as saying.

^{Sources: REUTERS, APE-MPE.}