In this Sept. 4, 2010 photo, people cross the border at the Zarbatiyah crossing southeast of Baghdad, Iraq.

Iraq’s interior ministry blamed Iranian authorities for allowing tens of thousands of Shi’ite Muslim pilgrims to storm a border crossing and enter the country without visas, in a rare public confrontation between the two neighbors.

The ministry said in a statement that the pilgrims, traveling on foot toward the Shiite shrine city of Karbala to take part in the annual Arbaeen religious ritual, overwhelmed security forces on Sunday, pulling down fences and injuring border guards.

It accused them of deliberately rushing the border crossing in order to pressure security forces to allow them to enter illegally, and it said the border guards had refrained from exercising their right to use force against them.

“We hold the Iranian side responsible because they did not fulfill their duties and obligations” to prevent those without visas from approaching the crossing, the ministry said.

Iraq’s Shiite-led government is heavily backed by Iran, which also provides training, arms and money to Iraq’s powerful Shiite militias, seen as a bulwark in the battle against ISIS militants in the country’s north and west.

Many leading Shiite politicians in Iraq including former Prime Minister Nuri al-Maliki developed close ties with Iran while living in exile there during the rule of Saddam Hussein, from the Sunni minority, who brutally repressed Shi’ites before he was toppled by the 2003 U.S.-led invasion.

Video posted online on Monday appeared to show hundreds of pilgrims dressed from head to toe in black forcing open a large gate and running through the checkpoint. Few security forces appeared to be present.

Reuters could not independently verify the footage.

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