Two Chinese and an Algerian abducted from a Sudanese oilfield have been released after two weeks in captivity, official media said on Friday.

The three men were kidnapped by "outlaws" in West Kordofan state on April 18, the SUNA news agency said.

It released a photograph of the trio disembarking from an airplane in Khartoum.

The Algerian and one of the Chinese men were dressed in blue coveralls of the type worn by oil technicians, while the other Chinese wore a T-shirt over blue coverall pants.

The Algerian smiled and waved, and one of the Chinese also sported a grin.

"Now they are in Khartoum," a Chinese embassy official told AFP, adding they had been freed on Thursday.

"They are in good condition. We talked with them," the official said.

SUNA quoted Oil Minister Makawi Mohammed Awad as saying five Sudanese petroleum technicians kidnapped at the same time as the foreigners were expected to be released by Saturday.

The embassy official said conflicting information has been provided about who abducted the men.

Anti-government rebels have periodically claimed attacks in the Muglad area of West Kordofan.

But a source familiar with the latest incident said various armed groups -- from militias to armed tribes and rebel splinter factions -- operate in the region.

Many might have an interest in detaining oil workers in search of money, the source said earlier.

Awad said negotiations were conducted with the kidnappers but no ransom was paid.

"The security authorities, the government of West Kordofan, the Ministry of Petroleum and (tribal) chieftains in West Kordofan state have released three foreign hostages," SUNA said.

The Justice and Equality Movement (JEM) rebels told AFP that a breakaway faction led by "Abu Kyan" kidnapped the oil workers.

"He is no longer part of JEM since 2011," JEM spokesman Gibril Adam Bilal said. "He is part of Sudanese militia."

Four government officials were killed during the attack on the oilfield, Awad said.

Algeria's foreign ministry announced earlier that, in addition to one of its nationals who was kidnapped, another was wounded during the initial assault.

According to the official from Beijing's embassy, the release occurred peacefully but the victims were not sure exactly who freed them.

"They told us someone got them out and some soldiers from the Sudanese army took them to another place," the official said, adding there were no details about their conditions during captivity.

She said the Chinese would rest in Khartoum for a few days before returning to their homeland.

Sudan produces 124,000 barrels of oil per day, according to President Omar al-Bashir.