Reports that an Iranian oil-tanker company has renamed at least 10 of its vessels and switched them to Tanzania’s flag to get round international sanctions sent shockwaves through the country’s leadership on Tuesday.

Government ministers and public officials went into overdrive following reports that the company had changed the registration of several of its ships and was now passing itself off as a Tanzanian firm. The vessels were apparently registered in Zanzibar.

The Minister for Transportation, Dr Harrison Mwakyembe, said he was aware of the development and had taken action. But his Foreign Affairs counterpart, Mr Bernard Membe, was in the dark about the saga.

The international news agency Bloomberg reported on Tuesday that the oil tanker company known as NITC, which is owned by the Iranian Pension Fund, has renamed at least 10 of its vessels and switched to the Tanzanian flag.

Mr Membe, who described the news as “shocking, strange and irregular according to the governing laws”, said thorough investigations would be conducted to establish the truth.

Bloomberg reported that NITC renamed five of its very large crude carriers, each holding about two million barrels of oil, and five Suezmaxes with a capacity for one million barrels.

Quoting the Equasis shipping database maintained by the European Commission, the reports pointed out that ownership of the ships was switched from NITC to new companies operating from the same address in Tehran. NITC remains the operator, though. All the ships were previously registered in Malta or Cyprus.

This development comes a few days before the full European embargo on Iranian crude exports, which starts next Monday, is extended to insuring vessels that carry the oil. Some 25 NITC tankers are being used to store crude, the Paris-based International Energy Agency said.

The US and Europe plan to impose the embargo on Iranian crude oil export amid fears that Iran nuclear programme is aimed at developing atomic weapons.

Mr Membe said: “That’s very strange and it’s irregular, in accordance with the governing laws. I will need to consult authorities in Iran for this matter.”

He spoke at Julius Nyerere International Airport shortly before boarding a plane for an official trip abroad. The minister has directed various departments to investigate how it was that a foreign company was able to fly a Tanzania flag on its properties.

Dr Mwakyembe said he was aware of the matter but did not have details, which he said the authorities were still working on.

Since the vessels were registered in Zanzibar, he added, it was important that his Zanzibari counterpart comment first.

“I can’t comment before the Zanzibar minister for Communication and Transport has done so,” he said. “Contact me after he comments.”

The Surface and Maritime Regulatory Authority (Sumatra) acting Director General, Mr Ahmad Kilima, echoed the sentiments but added that the Tanzania Maritime Act prohibits foreign companies from registering their ships in the United Republic. But Zanzibar, which has separate laws on the issue, does allow open registration.

Efforts to reach the Zanzibari minister, Mr Hamad Masoud, proved futile and the Zanzibar Maritime Authority (ZMA) boss, Mr Abdallah Hussein Kombo, would neither confirm nor deny the reports.

He did say, though, that Zanzibar’s Marine Act does not prohibit foreign companies from registering their vessels in the Isles.

“I can only confirm it if you send me the name of the ships and the company,” Mr Kombo said. “As for now, I am not aware of the news.”

But when contacted later, Mr Kombo denied knowledge of any transaction involving ZMA and NITC. He added: “We have not registered any vessel owned by NITC. Maybe the vessels were registered under another company’s name.”

Reported by Frank Kimboy and Mkinga Mkinga