دبلوماسية الناقلات: يواجه ترامب اختبارات من هافانا إلى هرمز

Energy shipments are increasingly being used as foreign policy tool as the Trump administration attempts to hold down two blockades on opposite sides of the globe.

The U.S., under the direction of President Donald Trump, has initiated a naval blockade targeting Iranian vessels in and around the strategically vital Strait of Hormuz, seeking to put economic pressure on Iran and bring an end to the Middle East crisis.

The move has prompted concern from China, given it has long been the largest buyer of Iranian crude, with Beijing calling the blockade "irresponsible and dangerous."

At the same time, the U.S. has imposed a de facto fuel blockade on Cuba, threatening to impose tariffs on any country that sends crude to the communist-run Caribbean island.

Russia, which has already breached the U.S. blockade by delivering a shipment of 100,000 tons of crude oil to the fuel-starved nation, has pledged to keep supplying Cuba with vital supplies of oil.

Sanctions experts and analysts say both blockades raise questions about the Trump administration's appetite for challenges to its maritime authority, particularly ahead of the U.S. president's summit with China's Xi Jinping next month.

Brett Erickson, a sanctions expert and managing principal at Obsidian Risk Advisors, said the prospect of a second Russian oil tanker reaching Cuba over the coming weeks is highly likely, highlighting the White House's own contradictions.

"When the Anatoly Kolodkin docked at the Matanzas oil terminal, it was in direct violation of U.S. sanctions. GL-134 had already been amended to GL-134A, which explicitly excluded deliveries to Cuba. Washington simply chose not to enforce it," Erickson told CNBC by email.

"Trump then publicly stated he didn't care whether Russia delivered to Cuba. Having made that statement and having declined to interdict, or even harass, the first vessel, it becomes politically untenable to now move against a second."

CNBC has contacted a White House spokesperson for the comment and is awaiting a response.

The U.S. blockade in the Strait of Hormuz, which started Monday, marked a sharp escalation in the conflict despite a pause in hostilities agreed April 7.

Trump suggested on Thursday, however, that the war in Iran could end "pretty soon." He also touted a second round of face-to-face negotiations between American and Iranian officials "probably, maybe, next weekend."

Trump-Xi talks

When it comes to the Strait of Hormuz, Erickson said the more dangerous escalation scenario here does not concern a Russian shadow fleet tanker, but rather a Chinese-linked or Chinese-flagged vessel carrying Iranian oil.

He pointed out that Treasury Secretary Scott Miller has said the U.S. will not renew a general license that the White House temporarily granted for the sale of Russian and Iranian seaborne oil during the Iran war. The license is poised to expire at 12:01 a.m. on Sunday.

From that moment, Erickson said Chinese refineries will once again be the overwhelming purchaser of any Iranian oil that is able to be exported.

"The logical Iranian move, from a pure statecraft perspective, is to test the blockade with a Chinese-linked or flagged tanker. That puts Washington in an extraordinarily precarious position: interdicting or boarding a Chinese-flagged vessel in the weeks before Xi-Trump talks would be an escalation of an entirely different order of magnitude. Being forced to sink a vessel would be unthinkable," he added.

'Fragile ceasefire situation'

China, which has long backed the regime in Tehran, has been sharply critical of the U.S. blockade in the Strait of Hormuz.

The Ministry of Foreign Affairs said earlier in the week that the targeted blockade of one of the world's most important oil chokepoints, coupled with an increase in military deployment, risked undermining an "already fragile ceasefire situation."

"While enforcing an undeclared blockade on Cuba, the United States allowed a Russian oil tanker to reach the island last month, apparently because Trump did not want a confrontation with Russia," Max Boot, a foreign policy analyst and senior fellow at the Council on Foreign Relations, said in an online article published Tuesday.

"Is he now prepared to risk a confrontation with Beijing, just as he prepares for a summit with Xi Jinping, if the U.S. Navy stops tankers ferrying oil to China?" he added.

The White House has said a highly anticipated meeting with China's Xi will take place in Beijing on May 14 and 15.

— CNBC's Hugh Leask contributed to this report.