More than a dozen Iran-flagged tankers have gathered off the coast of Sri Lanka as the US blockade all but halts access to Iranian ports six months into the war. Ship tracking data shows about 13 Iranian tankers anchored on the edge of Sri Lanka's territorial waters, alongside several others linked to Iran's "shadow fleet". They are prevented from returning to Iran by a US blockade on ships using Iranian ports, first imposed in April and reintroduced in July after the collapse of a month-long ceasefire.

"A flotilla of approximately 20 state-owned Iranian tankers, all empty of cargo, decided to seek shelter in the exclusive economic zone of Sri Lanka," said Samir Madani, co-founder of Tanker Trackers.com. The ships' draught levels indicated they were empty and therefore more likely to re-enter Iranian waters to pick up cargo, Madani said.

The US blockade has proven one of the most successful tools against Iran, preventing the country from importing fuel and earning revenue from oil exports. As of August 24, US forces said they had redirected 71 merchant vessels away from Iran, disabled three and boarded another two to ensure compliance. Since mid-July, no tankers bound for destinations beyond the Gulf have loaded at Iran's main oil-exporting facility on Kharg Island.

Analysts said the tankers off Sri Lanka were skirting territorial waters. In March, a US submarine sank the Iranian frigate IRIS Dena, some 19 nautical miles from the Sri Lankan coast. Sri Lanka's ports ministry and navy said they were unaware of Iranian tankers gathering off the country's coast.