KHARTOUM, Oct 6 (Reuters) - Relations between Sudan's north-south partners have deteriorated into a "poisonous" political atmosphere, U.S. envoy for Sudan Andrew Natsios said on Saturday.

A 2005 peace deal ended Africa's longest civil war in Sudan's south but the peace dividend promised has lacked focus because of global attention on a newer conflict in Sudan's western Darfur region, where a massive aid operation has diverted donor money earmarked for the south.

"We are deeply concerned with the health of the comprehensive peace agreement (CPA)," Natsios told reporters after a 10-day trip to Sudan.

"The current political atmosphere is poisonous ... this war of words has to stop," he added. He was referring to southern and northern officials using the media to accuse each other of failing to implement key clauses.

Last month South Sudan President Salva Kiir warned of a possible return to war if the deal was not implemented.

The north-south war claimed 2 million lives with 4 million driven from their homes, violence Natsios said was wore than in Darfur.

Natsios said many of the easy parts of the CPA had been implemented, but the harder protocols had not, including the redeployment of troops and reforming national security organs.

He said tension between the north-south partners was also partly due to the upcoming elections due in 2009.

"The people who are supposed to carry out the peace agreement are going to be likely opponents in the elections that are to be held in early 2009," he said.

Natsios added key protocols on demarcating the borders of the oil-rich contested Abyei region and mapping the north-south border needed to be resolved and offered U.S. help if needed.

But he said the partners needed to engage with one another to overcome the final obstacles to the deal.

"I've talked to both sides and urged them to step back from this spiralling public rhetoric," he said. "In private it's very acrimonious, poisonous is the word."

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