As the Obama Administration conducts its military withdrawal from Iraq, Iran has upped its involvement in the region, emphasizing how vulnerable American troops are now that forces are diminishing.

News broke this week that Iranian Revolutionary Guard forces carried out cross-border military operations in Iraq against guerrillas of the Party for a Free Life in Kurdistan (PJAK) less than a week after Iran warned that it reserved the right to attack the bases of the rebel Kurdish group. PJAK is an Iranian–Kurdish separatist group that carries out attacks in Iran from the Qandil Mountains along the Iraqi–Iranian border.

Tensions are mounting as Iran deploys an unprecedented 5,000 troops along its joint border with Iraqi Kurds. It is speculated that Iranians won’t cross the border as long as U.S. forces are present.

Although it wasn’t until 2009 that the Obama Administration blacklisted PJAK, Iranian forces have intermittently clashed with the Kurdish rebel group since its inception in 2004. However, Iran’s decision to shell PJAK bases in Iraq may be part of its broader campaign to destabilize and undermine U.S. efforts in Iraq.

Iran’s cross-border intervention is cause for concern, as this area is widely considered Iraq’s most stable area since the U.S. invasion. Tehran is also concerned over the future of Syria, its close ally, and views Western support of the opposition group there as a major threat to President Bashar al-Assad’s regime.

Iran’s attack in Iraq poses a threat to the region’s stability and America’s interests. Iran holds one of the most powerful military forces in the Persian Gulf region and thus would be in the best position to influence Iraqi decision-making absent a strong U.S. presence. As President Obama plans to withdraw troops by the end of the year, the United States needs to refocus its attention on the power dynamics in the Persian Gulf and make sure Iran does not use Iraq’s vulnerability to its advantage.