The Biden administration said on Monday that it is certain that Iran has been “facilitating attacks” against U.S. military personnel and bases around the Middle East.

During a regular press briefing, National Security Council Coordinator for Strategic Communications John Kirby said that over the past week, there has been “an uptick in rocket and drone attacks by Iranian-backed proxy groups against military bases housing U.S. personnel in Iraq and Syria.”

He also said that the White House is “concerned about the potential for any significant escalation of these attacks in the days ahead.”

The spokesman and retired U.S. Navy admiral also confirmed that while the Iranian military is behind the attacks, the government in Tehran seeks to “maintain some level of deniability.”