The Foreign Office has today warned Britons against all but essential travel to Sudan after widespread riots following the death of vice president John Garang in a helicopter crash.

More than 130 people have died in the unrest since the former rebel leader was killed in southern Sudan. Today President Yoweri Museveni of Uganda - the owner of the helicopter, and a friend of Mr Garang - appeared to inflame tensions further by saying that the crash may not have been an accident.

"Some people say accident, it may be an accident, it may be something else," President Museveni told a large crowd of mourners in Yei, where Mr Garang’s body was brought ahead of his funeral in Juba tomorrow

"The (helicopter) was very well equipped, this was my (helicopter) the one I am flying all the time, I am not ruling anything out. Either the pilot panicked... either there was some side wind or the instruments failed or there was an external factor."

It was the first time that an official of any government had suggested publicly that last Saturday’s crash may have been the result of foul play. An international panel of experts has been appointed to look into the crash.

Mr Museveni's comments were met with stony silence from the crowd, which had earlier greeted the arrival of Mr Garang’s coffin with wailing, ululation and prayer.

Salva Kiir, Mr Garang’s successor as chief of the Sudan People’s Liberation Movement/Army (SPLM/A), declined to comment on the remarks but said the group was eager to hear the results of the probe.

"All options are open and cannot be ruled out," he told reporters after calling on mourners to reject the violence that has engulfed parts of Sudan since Garang’s death and urging them to hold to their ex-leader’s vision for peace.

"Let us follow the footsteps of our leader. This is not the time for rioting," Mr Kiir added, blaming unspecified opponents of peace for wanting "to provoke a situation that would lead us back to war."

The Foreign Office statement warned against all but essential travel to Sudan, and against any travel whatsoever to the area near the border with Eritrea. The statement said: "As a result of the death of John Garang, the 1st Vice-President and leader of the SPLM/A on 31 July, the situation in Khartoum and in South Sudan is very tense.

"There have been demonstrations, numerous violent incidents and some deaths in and around Khartoum. Violence has spread to some other cities, and serious incidents have been reported in Port Sudan, Juba and Malakal. Tensions may be heightened as a result of Garangs’s funeral scheduled for 6 August. You should remain vigilant, and avoid demonstrations or similar large gatherings in public places and avoid all but essential travel in the place in which you are located."

It warns Britons in Sudan to be vigilant, and adds: "We strongly recommend that you obtain comprehensive travel and medical insurance before travelling. You should register with the British Embassy in Khartoum on arrival and keep in touch throughout your stay."

In Khartoum and Juba, senior SPLM/A officials cautioned against making any assumptions about the cause of the crash. "We don’t have anything to suggest it was caused by sabotage," SPLM/A spokesman Pagan Amun told AFP in Khartoum.

In Juba, SPLM/A General Pieng Deng told reporters that the flight data recorder from the helicopter had been recovered at the crash site. "Up to now we believe it is an accident but let the investigation end... as leaders, we cannot say anything until the investigation is concluded."

In Bor, Garang’s birthplace where his coffin was brought after Yei, a diplomat said that Mr Museveni’s remarks on the eve of the funeral were unfortunate, and noted that the Ugandan leader "is under personal pressure because it was his own helicopter".

Mr Garang and 13 others died when Mr Museveni’s presidential Mi-172 helicopter went down in the mountains of southern Sudan, sparking days of violence in Khartoum and the south that saw 130 killed and hundreds wounded. His death and the rioting raised fears that the landmark January peace deal he signed with Khartoum that ended Sudan’s 21-year north-south civil war would not unravel.

However, relative calm returned to the streets of Khartoum today as shop-owners reopened for business amid a noticeably lower security presence.

Many southerners believe Garang was somehow assassinated and have refused to believe the initial insistence of Ugandan, Sudanese and other officials that the helicopter went down because of poor weather. Mr Museveni did not elaborate on what he meant by an "external factor" but there has been widespread speculation in southern Sudan that the helicopter may have been somehow sabotaged or shot down.

In a bid to quell the speculation and restore calm, Sudanese President Omar el-Beshir has launched a formal probe that Museveni said would be joined by aviation experts from Uganda, Kenya, the United States, Britain and Russia.

Thousands of southern Sudanese descended on a former military training ground in Juba to help prepare Garang’s burial site ahead of his funeral on Saturday that is expected to draw some 500,000 people. Weeping women, stoic men and curious children converged on the site near the state parliament where frantic construction was underway on a mausoleum to hold Garang’s remains.

In accordance with Dinka tribal tradition, one of Garang’s sons, Chol, a 25-year-old fine arts student in Britain, dug up the first chunk of earth where his father will be laid to rest. "Sometimes I wake up and find people weeping," Chol said. "I never thought I would ever be digging my father’s grave."

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