Although the US government has not provided proof that the ships were carrying hidden missiles and other munitions, an informed official told CNN on Thursday that the freighters have been modified with large areas of their decks removed.
The official did not explain why these vessels would need to be altered to carry missiles.
Recent surveillance has shown some of those freighters moving in and out of Iranian ports in recent days, he added.
The Pentagon is yet to officially comment on the development.
Earlier this month, the US moved bombers and a carrier strike group into the region and fears of conflict have been stoked by a sharp increase in tensions between Tehran and Washington.
Iranian Islamic Revolutionary Guard Corps (IRGC) chief has warned on Wednesday Tehran was on a brink of a “full-scale confrontation with the enemy”, a day after nation’s supreme chief Ayatollah Ali Khamenei stated there would be no war with America amid tensions escalation.
The United Nations has called for “maximum restraint” from all parties amid heightened tensions between Iran and the United States and in the Gulf region.
“We are very concerned about the volatility of the situation. We call on everyone to exercise maximum restraint, prevent any escalation of and heightening of tensions,” Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres, told reporters on Thursday, Xinhua reported.
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- Iran on brink of ‘full-scale confrontation’ with enemy: IRGC chief Salami
- UN calls for ‘maximum restraint’ amid US-Iran heightened tensions