Iran's navy claimed to have successfully test-fired a medium-range missile from a vessel in the Sea of Oman on Sunday, just one day after its scientists said they had made a major breakthrough in the country's nuclear program.

The two developments ratcheted up tensions with the United States, where Republican presidential hopeful Rick Santorum said he would launch an attack on Iran's nuclear facilities if they refused the presence of arms inspectors.

Iranian TV said the missile test was conducted near the Strait of Hormuz, where ships transport 20 per cent of the world's oil supply. Iran's navy claimed that the surface-to-air missile, called the Mehrab, was designed to slip through radar undetected.

The test was part of a 10-day naval exercise, which has brought fears that Iran would disrupt oil tankers passing through the strait.

Iran has already threatened to close the strait if the U.S. imposes new sanctions against its oil exports. Last week, Iran's Adm. Habibollah Sayyari said closing the stretch of water would be "very easy."

Peter Jones, an expert on international politics and war studies with the University of Ottawa, said most analysts believe Iran has the means to follow through on its threat.

"I think a lot of people feel that they could do this for a short while, until the U.S. would force it open," he said.

On Sunday, Iran's navy appeared to soften its stance, saying it would not block ships during its naval exercise.

"We won't disrupt traffic through the Strait of Hormuz. We are not after this," said naval spokesperson Rear Adm. Mahmoud Mousavi, according to Iran's semi-official ISNA news agency.

However, lawmaker Ismail Kowsari said the naval exercise was preparation for closing the straight if more sanctions were brought against Iran.

"Iran's armed forces have practiced operations to close the Strait of Hormuz several times," Kowsari said, according to the Fars news agency.

"If we feel that the enemies want to prevent our oil exports, definitely we will close the Strait of Hormuz."

One day before Iran test-fired the Mehrab, its scientists said they had managed to build a nuclear fuel rod, a tube containing enriched uranium that feeds nuclear reactors. If confirmed, it would be a major step forward in the country's nuclear ambitions.

However, it's unclear whether Iran's first domestically built fuel cell contained enriched uranium when it was placed inside Iran's nuclear power research facility, or whether it was empty.

Iran is banned from buying fuel rods from any other country, as part of UN sanctions designed to stop its nuclear program. Iran says its nuclear program is for peaceful means -– simply to produce power and isotopes for cancer tests, not for nuclear weapons.