Defense Sec. Lloyd Austin told lawmakers on Thursday he shares their concerns over Iran’s shipment of arms currently bound for South America.

Two Iranian navy ships left port in Iran, believed bound for Venezuela, in May. The ships have rounded the Cape of Good Hope in southern Africa and are currently crossing the Atlantic.

Thursday marked the first time the Pentagon chief publicly commented on them, Politico reported.

At a Senate Armed Services Committee hearing Thursday, Sen. Richard Blumenthal, D-Conn., said that it would be “significant” on many levels if the ships were allowed to dock. Notably, he said, it would be the first time Iranian naval ships had been able to make the tough trek across the ocean.

“The precedent of allowing Iran to provide weapons to the region causes me great concern,” Blumenthal added.

“I am absolutely concerned about the proliferation of weapons, any type of weapons, in our neighborhood,” Austin agreed.

Austin wouldn’t say what type of weapons are on board the ships, but told Blumenthal he would tell lawmakers during a closed session.

Politico previously reported that U.S. intelligence has evidence that one of the ships, the forward staging ship Makran, has fast-attack boats on board it likely intends to sell to Venezuela. 

The White House has used diplomatic channels to urge Venezuela and Cuba to turn the ships away, while also saying the United States will take “appropriate measures” to prevent what it believes to be a “threat.”

“The delivery of such weapons would be a provocative act and understood as a threat to our partners in the Western Hemisphere” a senior administration official told Politico. “We would reserve the right to take appropriate measures in coordination with our partners to deter the transit or delivery of such weapons.”

After learning about the details in a classified setting, Sen. Marco Rubio, R-Fla., vice chair of the Senate Intelligence Committee, said, “The bottom line is, either [Venezuelan President Nicolás] Maduro should unconditionally turn them around, or we should force them to turn around.”

A top aide to Maduro has denied press reports that the ships will dock there. The official spoke on the condition of anonymity to discuss sensitive geopolitical issues.

During a news conference May 31, Iranian Foreign Ministry spokesman Saeed Khatibzadeh declined to say where the Makran was going.

“Iran is always present in international waters and it has this right based on international law and it can be present in international waters,” he said. “No country is able to violate this right, and I warn that no one makes miscalculations. Those who sit in glass houses should be careful.”

The fast-attack craft aboard the Makran are the type that the Guard uses in its tense encounters with U.S. warships in the Persian Gulf and its narrow mouth, the Strait of Hormuz. It’s not immediately clear what Venezuela’s plans would be for those ships.

“If the boats are delivered, they may form the core of an asymmetrical warfare force within Venezuela’s armed forces,” the U.S. Naval Institute said in an earlier published analysis. “This could be focused on disrupting shipping as a means of countering superior naval forces. Shipping routes to and from the Panama Canal are near the Venezuelan coast.”

The Associated Press contributed to this report.