A group of US Republican lawmakers have written to the White House expressing concern over reports that Iran was behind an attack on a US base in Syria last month.

Seventeen members of the House of Representatives in their letter urged the Biden Administration to “hold Iran accountable” for reportedly resourcing and encouraging the attack, a statement from Congressman Bryan Steil (R-WI) said Friday.

The lawmakers point to repeated attacks by Iran-backed groups on US bases in Iraq and in Syria this year and link the issue of Tehran’s behavior to talks in Vienna to revive the Joint Comprehensive Plan of Action, JCPOA. The Biden Administration’s policy is to revive the 2015 agreement in order to reestablish international controls over Iran’s nuclear program, but critics say that to achieve that, the United States must lift sanctions that would give Tehran more money to expand its influence in the region.

“We have continued to watch Iran attack US troops and our allies in the Middle East, while increasing its nuclear activities. These threats are ongoing, and your administration continues to weaken our ability to combat the Iranian regime by lifting US sanctions.”

Republican Representatives and Senators have written to the Biden Administration several times this year to warn against lifting the Iran sanctions. A letter in February by 15 Republicans drew Biden’s attention to “Iran’s malign activities, including its nuclear program,” missiles, as well as to its “support for terrorism, hostage taking, cyberattacks, and gross human rights violations.”

Former US president Donald Trump abandoned the JCPOA in 2018, saying it was a bad agreement that will not stop Iran from acquiring nuclear weapons in the future and demanding Iran to change its “malign behavior” in the region, as well as limit its missile development program and respect human rights.

Trump reimposed oil export and banking sanctions on Iran that had been lifted when the JCPOA was signed. This has pushed Iran’s economy to the brink of total breakdown, triggering high inflation and a large budget deficit.

The Republican lawmakers urged Biden not to reduce these sanctions, while Iran is suspected of orchestrating an attack against US troops.

“During a time of heightened tensions in the Middle East, it sends a dangerous message to our friends and adversaries that we continue to lift sanctions and negotiate with the largest state sponsor of terrorism as they attack us.”