By Maysam Behravesh

July 26 (Reuters) - Once again, the U.S. Navy has opened fire on an Iranian vessel in the Gulf. U.S. sailors fired warning shots Tuesday after the Iranian patrol boat – apparently operated by Iran’s Islamic Revolutionary Guard Corps (IRGC) – came within 150 yards of the USS Thunderbolt.

U.S. and Iranian ships have had tense encounters before, but these confrontations could become even more common - and potentially dangerous - if Washington intensifies its efforts to put more pressure on Tehran in general and the Revolutionary Guards in particular.

Donald Trump has made no secret of his desire to dismantle the Obama administration’s multilateral nuclear agreement with Tehran, describing it as “the worst deal ever.” On July 17, the U.S. president reluctantly certified, for the second time since his election, that Iran is complying with the terms of the nuclear pact known as the Joint Comprehensive Plan of Action (JCPOA).

A day later, his administration imposed new sanctions against Tehran over its ballistic missile program, targeting 18 new entities and individuals for involvement in what it described as Iranian “malign activities” in the Middle East. Those sanctioned included backers of the IRGC, Iran’s powerful military and security organization. Founded in the wake of the 1979 Iranian Revolution and acting independently of the regular army, the IRGC is also one of Iran’s most powerful economic institutions, controlling several of its strategic industries as well as some of its armed forces.

Washington’s ongoing efforts to put more pressure on the IRGC and proposals to designate it as a terrorist entity have raised tensions between the two old nemeses to a new level in the post-JCPOA era.

On the day that Trump confirmed Tehran’s nuclear observance, Iranian armed forces chief of staff Major General Mohammad Baqeri warned that incorporating IRGC in the blacklist of terrorist organizations could pose “a big risk for American and its bases and forces” in the region. In a similar reaction and shortly after the new U.S. penalties were announced, IRGC commander Major General Mohammad Ali Jafari warned that should Washington want to press ahead with the terrorist designation scheme, “it should dismantle its bases within up to 1,000 kilometers of Iran.”

Details of Tuesday’s maritime confrontation are still murky, and threatening bluster by officials on both sides is not new. However, the incident does underscore that Tehran can employ a number of options to jeopardize U.S. interests in the Middle East.

Though all American forces based in the wider region - from the Fifth Fleet in Bahrain to the Al Udeid Air Base in Qatar to the Bagram Air Base in Afghanistan - are within the reach of Iranian missiles, the IRGC is unlikely to deploy them in response to U.S. sanctions. Tehran’s military doctrine centers mainly on defense and a direct missile attack is not usually the IRGC’s modus operandi.

However, Tuesday’s incident underscores that the Revolutionary Guards can resort to aggressive behavior against U.S. vessels in the Persian Gulf. In the starkest instance, Guard members embarrassed Washington by seizing 10 American crew members from two Navy boats that blundered into Iranian territorial waters in January 2016.

The IRGC could also target U.S. forces without directly confronting them by deploying the proxy networks it has cultivated across the Middle East since the early 1980s. In the absence of reliable conventional allies, these networks typically form a key component of Iran’s “deterrence” strategy.

The IRGC has particularly close ties with Lebanon’s powerful Hezbollah group. Tehran has traditionally relied on Hezbollah to confront Israel, but has also used its fighters for high-profile missions. On 18 July 2012, a suicide bomb attack on a tourist bus in the Bulgarian resort of Burgas killed five Israelis. U.S. intelligence officials believe that the allegedly Hezbollah-led attack was retaliation for the assassination of Iranian nuclear scientists, which Tehran suspected was orchestrated by Israel.

The IRGC could also use its surrogates to exploit U.S. vulnerabilities in Iraq and Afghanistan.

Iraq’s predominantly Shia al-Hashd al-Shaabi or Popular Mobilization Forces (PMF), with an estimated force of over 60,000 fighters, includes groups that are heavily backed and influenced by Iran, including the Badr Organization, Kata’ib Hezbollah and Asa’ib Ahl al-Haq that many in Washington believe were behind deadly rocket attacks and roadside bombings that killed hundreds of American forces during the U.S. occupation of Iraq.

Tehran could also increase the pressure on American forces in Afghanistan by doubling down on military backing of the Taliban. As tensions have flared between the United States on the one hand and Iran and Russia on the other, the latter have already boosted support for the Taliban insurgents.

With the growing engagement of the United States in the Syrian civil war under the Trump administration, Tehran could pursue a similar course in Syria too. U.S.-backed forces fighting Islamic State militants in the northeastern and eastern regions of the country would be particularly vulnerable.

A Washington designation of the IRGC as a terrorist entity is unlikely to restrain the group. On the contrary, the label could even embolden the Corps to behave more aggressively by removing its reason for restraint. And that, in turn, could further destabilize the region.

(Maysam Behravesh is an affiliated researcher at the Center for Middle Eastern Studies, Lund University, Sweden. The opinions expressed here are his own.)