Francis Mwanza, the UN World Food Programme information officer in Rome, said that on 27 July the Briton, whom he refused to name, a Ugandan and a Sudanese escort were returning from the town of Bahr el Ghazal when they were stopped for 45 minutes at a police checkpoint in the town of Lainya.
The WFP workers felt a burning sensation and began vomiting. The town, in the rebel-held area of Eastern Equatoria province, had apparently been bombed four days earlier by the Sudanese air force.
A spokesman for the rebel Sudan People's Liberation Army (SPLA), Samson Kwanje, said last week a government aircraft dropped 16 bombs in Lainya and six in nearby Kaaya on 23 July, the day unsuccessful peace talks ended in Kenya.
"It is reported that a day after the bombing of these towns, children and men and women started to vomit blood," Mr Kwanje said. Since the bombing "almost all pregnant women have aborted or are gravely ill", he said, and goats, sheep, cats, dogs and birds were dying.
Sudan rejects the claims. The pro-government Akhbar Al-Youm newspaper quoted an army spokesman, General Mohamed Osman, saying the reports were a smear against the Khartoum government.
Tarik Bakhi, a diplomat at Sudan's mission to the UN, said his country had recently signed the Chemical Weapons Convention and had nothing to hide. "We categorically deny the allegations. I don't think Sudan will mind an investigation."
Lindsey Davies, a spokeswoman for the WFP in Nairobi, said the UN intended to investigate. "We are taking this very seriously," she said, describing the symptoms. "There was a very bad smell in the area coming from a bomb crater 10 metres away." Mr Mwanza said the Briton was in hospital in Nairobi having tests yesterday.
Sudan's 16-year civil war has left 1.9 million dead from violence and famine. The SPLA is fighting the Islamic-led government for control of the Christian south. The latest ceasefire collapsed on 15 June.
Last August President Bill Clinton ordered cruise missiles to be launched at a pharmaceutical factory near Khartoum suspected by the US of making nerve agents.
So far the US has failed to provide compelling evidence that the plant made chemical weapons.
Experts said some symptoms described were similar to those of mustard gas. "Nerve agents are referred to as nerve gases, but in fact they are liquids and they evaporate," said Greg Jones, a Rand Corp expert on chemical weapons. "They would have dissipated in a few hours under the hot Sudanese sun."
The Foreign Office said last night that Britain would be looking into the reports with some urgency through the embassy in Khartoum.Reuse content