U.S. Representatives Peter J. Roskam (R-IL) and Ted Deutch (D-FL) sent a letter to Secretary of State Rex Tillerson and Secretary of Defense James Mattis, on Thursday, May 25, urging them to take all necessary action to prevent Iran from establishing a permanent military presence in Syria.

On the same day, a U.S. Senate committee approved legislation that would authorize the Trump administration to put new sanctions on Iran over its ballistic-missile program, support for Islamist militant groups, and other actions.

In the letter, the lawmakers wrote:

“The Islamic Republic seeks to solidify its access to the Mediterranean Sea by building a permanent seaport and constructing numerous military installations throughout the country. A permanent Iranian military presence in Syria would greatly harm U.S. interests in the region and decrease the likelihood of reaching a political agreement to end the Syrian civil war.”

Reps. Roskam and Deutch also emphasized the need for measures to disrupt the shipment of personnel and military supplies to Syria via commercial aircraft by holding accountable Iranian airliners found to be providing support to the Assad regime or terrorist organizations.

In January, Rep. Roskam introduced the Terror-Free Skies Act to curb the use of commercial aircraft in support of international terrorism.

Iran claims its presence in Syria is justified because the government of Bashar Assad has requested assistance. However, a serious belligerency by rebels and credible reports on repeated war crimes involving Assad's troops and its allies, weaken such claims based on international law.