An Iranian naval officer has said a number of warships had been ordered to approach US maritime borders as a response to the stationing of US vessels in the Gulf, the semi-official Fars news agency reported.

"Iran's military fleet is approaching the United States' maritime borders, and this move has a message," the agency quoted Admiral Afshin Rezayee Haddad as saying on Saturday.

Haddad, who is described as the commander of the Iranian navy's northern fleet, said the vessels had started their voyage

towards the Atlantic Ocean via "waters near South Africa", Fars reported.

Fars said the plan was part of "Iran's response to Washington's beefed up naval presence in the Persian Gulf".

The report, which carried no details of the vessels, could not be confirmed independently.

The Reuters news agency quoted an anonymous US defence official as casting doubt on the Iranian claims.

But the official added that "ships are free to operate in international waters".

The US and regularlys stage naval exercises in the Gulf, saying it wants to ensure freedom of navigation in the waterway, through which 40 percent of the world's seaborne oil exports passes.

The US bases its Fifth Fleet in Bahrain.

Iranian officials have often said Iran could block the Strait of Hormuz, at the mouth of the Gulf, if it was attacked over its disputed nuclear programme.

Fars said the Iranian navy had been developing its presence in international waters since 2010, regularly deploying vessels in the Indian Ocean and the Gulf of Aden to protect Iranian ships from Somali pirates.

Missile tests

Hard-line Iranian MPs meanwhile have accused the president, Hassan Rouhani, of halting a scheduled missile exercise, the state news agency said Sunday.

IRNA reported that 24 members of parliament said in a statement that the Supreme National Security Council, headed by the president, stopped the annual test and did not approve its budget.

Hard-liners are at odds with Rouhani and his foreign minister, Javad Zarif, over their policy of outreach to the West.