Its main crude export hub, Kharg Island terminal, has stoped circulating a list of loaded oil tankers at the anchorage citing security reasons, industry sources said.

"The terminal is not releasing any information for vessels loaded and at the anchorage due to security reasons," an email from a Kharg Island-based shipping agent said.

A loading programme dated June 13 obtained from the terminal only showed one oil tanker of unsold crude at anchor as opposed to 20 in mid-May.

But a senior NITC source said the number of NITC tankers used as floating storage was "pretty much unchanged" compared with May 14, when the list of tankers at anchor was still available and showed twenty loaded oil tankers storing around 35 million barrels of crude oil.

Fifteen of NITC's fleet of 25 very large crude carriers (VLCC) were allocated to store crude at anchor, each loaded with about 2 million barrels of crude. Another five of Iran's nine Suezmax tankers, with capacity of one million barrels, were also being used as floating storage.

"The difficulties in payments, getting insurance are still continuing," the NITC source said.

Several customers of Iranian crude including some oil companies in Europe like Total SA and Hellenic Petroleum have already stopped buying ahead of an oil embargo by the European Union due to start on July 1, also including a ban on EU insurance firms covering Iran's exports.

NITC already lost its ship insurance cover from European providers last year due to Western sanctions imposed on Iran. It secured alternative cover mainly in Asia and also in Iran from privately owned Kish P&I.

 The EU in January embargoed purchases of Iranian crude but let those with existing contracts continue importing until July 1. The West suspects Iran is trying to develop atomic bombs, while Iran says its nuclear work is solely for civilian purposes.

Crude exports from OPEC's second largest producer have fallen by around 30 percent to around 1.5 million barrels per day (bpd) from around 2-2.2 million bpd last year, despite contradicting comments from Iranian oil minister who said last week that exports were steady.

 Iran and China remain the biggest buyers of Iranian crude and they are unlikely to be deterred, the NITC source said. "China and India are not worried...China has strategic interest in Iran," he added.

The United States added last week India to a list of countries exempt from US sanctions due to start on June 28 but fell short of doing so for China, Tehran's biggest oil customer.