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More than 300 people have now died from cholera in earthquake-ravaged Haiti, as investigators from the UN probed a suspected source of the outbreak.

With cases confirmed in four out of the country's 10 departments, authorities were fighting on Thursday to stop the disease from taking a firm hold in the capital, Port-au-Prince.

But the confirmation of the death toll came amid a UN investigation into samples of a suspected sewage spill leaking behind a Nepalese peacekeeping base in Haiti towards an infected river system.

UN officials appeared to take away samples from the site on Wednesday, following accusations that the spill could be the source of the cholera outbreak,

Vincenzo Pugliese, a mission spokesman, confirmed on Wednesday that the UN team was testing for cholera - the first public acknowledgement that the 12,000-member force is directly investigating allegations its base played a role in the outbreak, the Associated Press news agency reported.

Al Jazeera's Sebastian Walker, reporting from Port-au-Prince said the UN is "categorically denying" that peacekeepers were the cause of the outbreak.

"But you know, that river, from that base, flows into the town of Mirebalais," he said.

"In Mirebalais there have been many cases of cholera. There's 50 at the local prison there, there have been cases throughout that department - that's the central department. That river then runs on into the Urbanite, which is the heart of where the cholera has been raging over the past few days."

Suspected Nepal connections

The Nepalese mission strongly denies its base was a cause of the infection.

Pugliese said civilian engineers collected samples from the base on Friday which tested negative for cholera and the mission's military force commander ordered the additional tests to confirm. He said no members of the Nepalese battalion have the disease.

But local politicians, including a powerful senator and the mayor of Mirebalais, are pointing the finger at the Nepalese peacekeeping base, which is perched above a source of the Meille River, a tributary to the Artibonite River on Haiti's central plateau.

Cholera is endemic to Nepal, which suffered outbreaks this summer. A recent article in the Japanese Journal of Infectious Diseases about outbreaks in 2008-09 said the strain found by researchers was "Vibrio cholerae O1 Ogawa biotype El Tor", the same strain found in Haiti. 

However, Eric Mintz, an epidemiologist with the US Centers for Disease Control and Prevention told the Associated Press that the strain is too common to be considered a "smoking gun".

Meanwhile the epidemic continued to spread, with cases confirmed in two new departments in Haiti's north and northeast, Imogen Wall, a spokeswoman for the UN office for the co-ordination of humanitarian affairs said.

Our correspondent reported that there are 174 suspected cases of cholera infection in a town just an hour outside Port-au-Prince, where the disease has not yet spread.

International aid workers and the UN are focusing their efforts on stemming the spread of the outbreak, which was first noted on October 20.

Source: Al Jazeera and agencies