NEW YORK, April 14 -- Iran slammed a US blockade around its ports on Monday as a "grave violation" of its sovereignty, as Washington and Tehran's belligerent rhetoric rattled a fragile truce.

"The imposition of a maritime blockade constitutes a grave violation of the sovereignty and territorial integrity of the Islamic Republic of Iran," Iran's ambassador to the United Nations Amir Saeid Iravani wrote to UN Secretary General Antonio Guterres, in a letter seen by AFP.

The "unlawful" blockade also "constitutes a serious violation of the fundamental principles of the international law of the sea," Iravani added.

US President Donald Trump ordered a blockade of ships entering or leaving Iranian ports and coastal areas in the Gulf Sunday, fo...