Anti-terrorist officers were today searching a cargo ship seized in the English Channel in what Scotland Yard described as a "major security operation".
They swooped on the MV Nisha at 8am along with the Royal Navy and Customs and Excise after an intelligence-led initiative.
British ships were waiting for the cargo ship when it arrived in the Channel.
Security sources said they were "acting on intelligence" that the vessel was carrying "terrorist material" but there was no specific intelligence that anthrax was involved.
A Scotland Yard spokesman said the ship was being inspected and the crew, thought to be Indian, was currently being interviewed and "co-operating fully".
The ship had sailed from Mauritius and was believed to be carrying a cargo of sugar, he said.
It was intercepted off the Sussex coast, about 30 miles south of Beachy Head, according to reports.
The Ministry of Defence said it was travelling west to east through the Channel.
There was no immediate danger to people living in the area, according to Scotland Yard.
The ship was boarded in international waters in accordance with international law, a police spokesman said.
"At this stage it is not possible to say how long officers will remain aboard the vessel or how long the inspection will take to complete," he added.
HMS Sutherland was involved in the operation, the Ministry of Defence said.
The operation came just two days after eight suspected terrorists were rounded up under new anti–terrorism laws in London, Birmingham and Luton.
Suspects are being held in high-security jails in London and Milton Keynes.
The MV Nisha was heading for the Tate & Lyle sugar refinery at Silvertown in east London, according to the company.
She was carrying 26,000 tonnes of raw sugar owned by the Mauritius Sugar Syndicate, said director of corporate communications Chris Fox.
The vessel had been chartered by the syndicate and was due to arrive at 4am tomorrow. The sugar was then to be refined by Tate & Lyle.
"We are co-operating fully with the anti–terrorist branch and are doing everything we can to help them," Mr Fox said.
"All they need now is the time to search the ship. There was a lot of secrecy around it all so we only heard about it this afternoon."
A spokesman for the Port of London Authority confirmed the vessel had been headed for the refinery on the Thames.
"As the port authority involved, we were aware that Special Branch were watching her and were told that she had been seized," he said.
Scotland Yard could not confirm whether the ship had stopped off in Djibouti, next to Somalia, which has been linked with Osama bin Laden's al-Qa'ida network.Reuse content