Pompeo said on Saturday he sent a letter to Iranian Major General Qassem Soleimani and Iranian leaders expressing concern regarding Iran’s increasingly threatening behavior towards Iraq, the Reuters reported.

Speaking during a panel discussion at the annual Reagan National Defense Forum in Southern California, Pompeo said he sent the letter after the senior Iranian military commander had indicated that forces under his control might attack US forces in Iraq.

However, He did not specify the date.

“What we were communicating to him in that letter was that we will hold him and Iran accountable for any attacks on American interests in Iraq by forces that are under their control,” Pompeo told the panel.

“We wanted to make sure he and the leadership in Iran understood that in a way that was crystal clear.”

Soleimani, who is the commander of foreign operations for Iran’s elite Revolutionary Guards, refused to open the letter, according to Pompeo, who took over the CIA in January.

Reuters reported in October that Soleimani had repeatedly warned Kurdish leaders in northern Iraq to withdraw from the oil city of Kirkuk or face an onslaught by Iraqi forces and allied Iranian-backed fighters and had traveled to Iraq’s Kurdistan region to meet Kurdish leaders.

The presence of Soleimani on the frontlines highlights Tehran’s heavy sway over policy in Iraq and comes as Shi‘ite Iran seeks to win a proxy war in the Middle East with its regional rival and US ally, Sunni Saudi Arabia.

A US-led coalition has been fighting Daesh in Iraq and Syria and is often in proximity to the Iran-allied militia fighting Isis there.

“You need to only look to the past few weeks and the efforts of the Iranians to exert influence now in Northern Iraq in addition to other places in Iraq to see that Iranian efforts to be the hegemonic power throughout the Middle East continues to increase,” Pompeo said.