Iraq closed its southern Shalamcheh border crossing with Iran to travelers from both countries on Saturday, an Iraqi security source and Iranian diplomat said.
The security source said Tehran had demanded the closure because of ongoing public protests in both Iran and Iraq. The border would remain shut until further notice but would not affect goods or trade, they added.
Iraq has been engulfed in a month-long protest demanding government change.
Oil-rich Iraq is OPEC's second biggest producer, but one in five people live in poverty and youth unemployment stands at 25 percent, according to the World Bank. Those staggering rates sparked the first wave of protests on October 1, and public anger quickly spiraled into calls for an overhaul of the entire ruling system.
It is the biggest and most complex challenge in years to the political order and around 300 people have been killed in protests.
Protesters say the current framework allows political parties to dole out government jobs based on affiliation and bribes, choking out independents in a country with a weak private sector. They are demanding profound reform and constitutional amendments.