The United States’ plan to blockade Iranian ports and marine traffic has sent oil prices surging, as the countries reignited their tussle over the crucial Strait of Hormuz after peace talks ended without a deal.

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American forces began enforcing the blockade at 10 a.m. ET Monday after President Donald Trump vowed to block “any and all Ships from trying to enter, or leave” the strait, which he had spent weeks pressuring Tehran to reopen.

The current two-week ceasefire came into force after Trump threatened to obliterate the “whole civilization” of Iran if it did not reopen the waterway, through which some 20% of the world’s oil passes.

The announcement of the blockade sent stocks falling and the price of crude oil soaring to above $100 amid questions around why the U.S. might cut off a trade route it had been trying to force open, how the blockade would work and what it could mean for countries across the world.

U.S. Central Command, or CENTCOM, clarified Trump’s Sunday comments, saying the blockade would only impact maritime traffic entering and exiting Iranian ports. It stressed that U.S. forces would not “impede freedom of navigation” for vessels transiting the strait to and from other ports.

CENTCOM said the blockade on the key trade route would be enforced “impartially” against any and all vessels entering or departing Iranian ports, including those on the Persian Gulf and the Gulf of Oman.

The U.S. began mine-clearing efforts over the weekend. The commander of CENTCOM, Adm. Brad Cooper, said U.S. forces would begin the “process of establishing a new passage” that would be shared “with the maritime industry soon to encourage the free flow of commerce.”

The U.S. moves come after Iran's own blockade of the strait not only sent energy prices up, but also increased the price of fertilizer and threatened the economies of countries worldwide.

Tehran has repeatedly ignored Trump's demands that it reopen the waterway, and instead began charging some ships millions of dollar to transit Hormuz.

CENTCOM said it would reveal more information on its plans to commercial mariners through a formal notice before the blockade started Monday.

Iran’s Revolutionary Guard, meanwhile, warned that any military vessels attempting to approach Hormuz would be considered in violation of the ceasefire deal agreed to between Washington and Tehran and would receive a firm response.

Iran's armed forces said the blockade amounted to "piracy."

Enforcing the U.S. blockade will be a complicated, "high-risk" and legally contentious endeavor, said Andreas Krieg, a senior lecturer at King’s College London’s School of Security Studies.

"Practically, this would look less like a clean historical blockade and more like a messy, high-risk interdiction regime," he said.

The U.S., he said, would need to identify, track, hail, divert and maybe even board vessels linked to Iranian ports, all while “operating in one of the most crowded and politically sensitive waterways in the world.”

By early Monday, hours before the blockade was set to come into effect, ships appeared to be largely steering clear of the strait, with significantly fewer ships in the area compared to the day prior, real-time and historic vessel tracking provided by Kpler showed.

Outside of ships proactively avoiding the strait, Krieg said, enforcement would likely rely on a mix of naval patrols, surveillance, maritime warnings, allied intelligence and selective interdiction. He said that could even involve the boarding of ships, as was seen in Venezuela.

“Bandwidth” could become a real issue for the U.S., while mine-clearing efforts could put American ships at risk, he said.

CENTCOM has said it had begun “setting conditions for clearing mines” in the strait Saturday, with two U.S.-Navy guided missile destroyers deployed in the operations.

If the blockade is successful in cutting off Iran’s oil flows, it could have a crippling effect on the Islamic Republic, which is extremely reliant on its oil exports.

Countries like China, which imports nearly a third of its oil through the strait, could also be hit hard, with a prolonged conflict “actively affecting China’s domestic consumption,” including oil prices, said Zhu Feng, dean of the School of International Studies at China’s Nanjing University.

Guo Jiakun, spokesperson for the Chinese Foreign Ministry, on Monday urged the U.S. and Iran to "remain calm and exercise restraint," saying "the way forward is to achieve an early ceasefire and an end to hostilities."

Meanwhile, Mukesh Sahdev, chief oil analyst at XAnalysts, said, the U.S. should ultimately be able to withstand higher gas and oil prices better than Iran can weather a major blow to its export income. If successful, he said the blockade could prove to be a "master stroke" in the conflict with Iran.

Still, Washington's blockade could not only be a high-risk endeavor, but also a legally "contentious" one, Krieg said.

"A blockade is one of the most escalatory tools a state can use at sea, and its legality depends on context, proportionality, discrimination and the underlying state of armed conflict," he said.

Chantal Da Silva reports on world news for NBC News Digital and is based in London.

Mithil Aggarwal is a Hong Kong-based reporter/producer for NBC News.