US national security authorities are monitoring two Iranian ships believed to be heading to Venezuela, in a new Iranian provocative move at a time of tension in relations between Washington and Tehran.

Politico quoted three people familiar with the situation, who refused to reveal their identities, as saying that an Iranian frigate and a former oil tanker "Makran" had been converted to a floating base, heading south along the east coast of Africa.

The site's sources indicated that US officials do not know the exact destination of the two ships, but they believe that they may eventually head to Venezuela.

Iran and Venezuela have established close relations over the past years, and their cooperation includes gasoline shipments, joint ventures for car and cement factories, and are both subject to US sanctions.

The report said that senior officials in President Nicolas Maduro's government had been told that welcoming Iranian warships to Caracas would be a mistake, according to a person familiar with the discussions, but it was unclear whether Maduro had heeded the warning.

The website added that US officials monitored the ships' rotation, but as of Friday morning they were still sailing south.

And the website quoted an informed source that US lawmakers have been informed over the past few days that Washington believes that the two ships are heading towards Venezuela, although they indicated that the destination may change.

The site's report indicates that the presence of Iranian ships in America's backyard will pose a challenge to Washington in the region, and is likely to fuel the debate about President Joe Biden's reopening of negotiations with Iran.

Iranian media had previously claimed that the 230-meter Makran ship, which was commissioned this year, could serve as a platform for electronic warfare missions and special operations. It is capable of carrying six to seven helicopters, as well as drones, according to Iranian media.

The website's report said that the timing of the Iranian move was not appropriate for those who hope to reduce tension with Tehran.

It is noteworthy that Iran and the major powers involved in the 2015 agreement have been in talks in Vienna since early April, seeking to revive the agreement that the United States unilaterally withdrew from in 2018 during the term of its former president, Donald Trump, re-imposing harsh economic sanctions on Iran.