The timing of this American escalation is noteworthy for several reasons.

First, it comes just weeks after US warships in the Mediterranean fired 59 Tomahawk cruise missiles against Assad’s Shayrat airbase, which Western intelligence agencies allege was used to launch a deadly chemical weapons attack in northern Syria. That intervention was the first time the US directly attacked the Syrian government.

Second, the al-Tanf skirmish comes just hours after President Donald Trump is scheduled to depart Washington for a tour of the Middle East, his first overseas trip since assuming office. He will travel to Jerusalem and Riyadh, Saudi Arabia where he is expected to reassure Israel and America’s Sunni Gulf allies that his administration is committed to containing and deterring Iran, now the principal security underwriter of the Assad regime in Syria.

Third, the US Treasury Department on Wednesday sanctioned two senior Iranian officials, one of whom, the department said in a press statement, “facilitated the sale of explosives and provided other support to Syria.” The other was “the director of the organization responsible for Iran’s solid-fueled ballistic missile program.”