Chinese-made bullets and aircraft bought from Russia are used to commit rights violations in Sudan's Darfur under an ineffective U.N. arms embargo, Amnesty International said on Thursday.

The London-based rights watchdog aired similar concerns five years ago but its latest report comes after "a new wave of fighting" between opposition groups and government forces over the past year.

A group of Chinese workers "kidnapped" by rebels in southern Sudan 11 days ago have been freed and flown to Kenya, the foreign ministry said on Tuesday.

"The Sudanese authorities allowed a Red Cross plane to take them from Kauda to Nairobi ... this Tuesday morning where they were given to the Chinese embassy there," the statement said.

Sudan is closer to war than peace with the breakaway state of South Sudan, President Omar al-Bashir said on national television Friday, with a dispute over oil and other issues stoking tensions.

"The climate now is closer to a climate of war than one of peace," he said.

Dozens of people were killed in South Sudan during a shootout at a peace meeting to resolve disputes about stolen cattle, with some reports claiming as many as 37 people died, officials said Friday.

"These guys just started shooting everywhere," said Gideon Gatpan Thoar, Unity state information minister, reporting 37 people killed in Wednesday's attack.

China said Wednesday that 25 Chinese workers kidnapped by Egyptian Bedouins demanding the release of their Islamist relatives had been released.

The incident comes days after 29 Chinese nationals in Sudan were captured by rebels who attacked their camp in the volatile South Kordofan state, where they were involved in a road-building project. They have still not been released.

None of the 29 Chinese workers abducted after an attack in a volatile region of Sudan have been freed, Chinese state media said Tuesday, dismissing reports that some of the workers had been released.

The workers were abducted Saturday by militants in a remote region in the country's south. Sudanese state media reported Monday that 14 of them had been freed, but the official Xinhua News Agency and China Daily newspaper said all 29 were still being held.

Up to half a million starving refugees could flee violence in Sudan within months, sparking a massive food crisis in newly independent South Sudan, the U.N.'s World Food Program (WFP) has warned.

WFP's Deputy Executive Director Ramiro Lopes da Silva said relief agencies were preparing for the worst, with Sudan's government in Khartoum blocking emergency aid into border regions where it is battling rebel forces.

Twenty-nine Chinese workers described as hostages by Sudan's military are in good shape and will be released when the security situation allows, their rebel captors told Agence France Presse on Monday.

"They are okay. They are doing well," said Arnu Ngutulu Lodi, spokesman for the Sudan People's Liberation Movement-North (SPLM-N) in South Kordofan state.

South Sudan on Monday accused its former foes in the Khartoum government of arming gunmen who killed over 40 people in a cattle raid, as the U.N. warned tensions between the two sides risk regional peace.

"A militia group from Unity state penetrated into Warrap state... and attacked people in a cattle camp, killing over 40," said Interior Minister Alison Manani Magaya, the latest wave of violence in the world's newest nation.

U.N. chief Ban Ki-moon warned Sunday that a furious row between Sudan and South Sudan threatened regional security.

Ban said both Sudanese President Omar al-Bashir and his South Sudan counterpart Salva Kiir lacked the "political will" to tackle border and oil disputes since the South seceded last July.