Foreign Policy | Lara Seligman: As U.S. President Donald Trump’s administration ratchets up pressure on Iran, the U.S. Defense Department is warning Moscow and Tehran against cooperating in the Middle East, a relationship that a senior Pentagon official said could further destabilize the region.

During a May 30 event in Washington, D.C., Kathryn Wheelbarger, the acting assistant secretary of defense for international security affairs, warned of Russia and Iran’s creeping influence in the Middle East, saying both have “revisionist ambitions” that will negatively impact U.S. partners in the region.

“Even understanding historical mistrust between Moscow and Tehran, the United States and the region must be mindful when revisionist powers cooperate,” Wheelbarger said. “We are watching this relationship closely.”

She also harshly criticized Russia, continuing the administration policy of delivering rhetorical blows to Moscow even as Trump has often been reluctant to criticize Russian President Vladimir Putin personally. Wheelbarger painted Russia as an unreliable and dishonest partner and said Moscow’s relationship with Iran in particular is an example of this duplicity.

“Russia’s attempts to be amenable to all regional players—irrespective of regional animosities and conflicting national interests—is a strategy likely to create implicit distrust and distance,” Wheelbarger said. “By striving to accommodate all sides in regional disputes, Russia shows it cannot be trusted when true choices need to be made or friends need to be known.”

Wheelbarger’s comments, which appear designed to drive a wedge between Iran and Russia, an influential player in the Middle East, come as the Trump administration aims to squeeze Tehran economically and militarily. One year after withdrawing from a landmark 2015 nuclear deal, the United States has in recent weeks reimposed sanctions, blacklisted Iran’s Islamic Revolutionary Guard Corps as a terrorist group, and deployed additional troops and military equipment to the Persian Gulf in response to an unspecified threat.

U.S. National Security Advisor John Bolton, who has previously called for the overthrow of the “mullahs’ regime” in Tehran, claimed without evidence this week that Iran was behind a May 12 attack on four commercial ships in the Gulf of Oman. Tehran has repeatedly denied any involvement in the incident.

Russia appears mindful of U.S. concerns about its relationship with Iran. Moscow reportedly rejected Tehran’s request to buy the S-400 missile defense system over worries the sale would stoke more tension in the Middle East.

Mark Katz, a professor at George Mason University, warned that U.S. regional partners that are hoping that Moscow will limit Tehran’s actions in the Middle East will likely be disappointed. The two nations are already working together in the region, he stressed.

“We need to convince both our Middle Eastern allies and also elsewhere that Russia and Iran together are a problem for us,” Katz said. “Those in the Middle East concerned about Iran need to understand that working with Russia is not necessarily going to help them with Iran.”

Wheelbarger also noted that Russia’s military has significant limitations, pointing out that even for those countries it has promised to defend, Moscow avoids “real military confrontation.” For example, Israel’s military strikes in Syria continue to degrade Iranian positions; meanwhile, Russia failed to contest U.S. strikes on Syria in response to the regime’s use of chemical weapons.