BEIJING, Oct 30 (Reuters) - China sent a team of officials to Sudan on Thursday to seek the release of kidnapped oil workers in the disputed aftermath of rescue efforts after four Chinese hostages were killed.

Officials from the Foreign Ministry, Commerce Ministry and China National Petroleum Corpn (CNPC) left Beijing to "negotiate with the Sudanese side on all-out efforts and measures of rescuing a worker still missing", Xinhua news agency reported. But other Xinhua reports said two were still missing.

The move appeared to be an attempt to bolster control of a standoff that went badly wrong on Monday, when the four kidnapped Chinese oil workers died in a clash between their captors and Sudanese forces.

They were in a group of nine Chinese nationals working for CNPC kidnapped over a week ago. Three of the men are in hospital after being rescued, Xinhua reported.

But there are conflicting claims about how many remain missing. Chinese officials had said one man was still being held, but Xinhua reports from Khartoum late on Thursday said "two hostages are still missing".

An official from the Chinese Foreign Ministry spokesman's office could not say which number was correct. "We're also trying to clarify the situation and will issue a statement when we can," said the official, who did not give his name.

The killings and confusion have cast a shadow over Beijing's ties with the oil-producing African country, where China is a key investor and supplier of arms.

The oil workers were snatched near a small oilfield where they were doing contract work for the Greater Nile Petroleum Operating Company (GNPOC). The company is a consortium, led by China's CNPC, that includes India's ONGC, Malaysia's Petronas and Sudan's state-owned Sudapet.

Human rights groups accuse China of doing too little to help stop bloodshed in Darfur, an ethnicly mixed region where the Sudanese army and government-backed militias have been fighting rebels, leaving many civilians dead and displaced.

China says its investments and diplomatic efforts are helping the people of Sudan, including Darfur.

Sudanese officials said the gunmen were members of the Darfur rebel group the Justice and Equality Movement (JEM). But that group has denied any involvement. JEM kidnapped five oil workers in the region last year but later released them unharmed.

Sudanese officials first said that five hostages died on Monday, a figure first echoed by Chinese officials. Then the Chinese Foreign Ministry said on Tuesday that four were killed in a failed rescue effort. (Reporting by Chris Buckley; Editing by Nick Macfie)

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