SYDNEY, Australia (CNN) -- Gunmen believed to be UNITA rebels ambushed and killed a Briton, a Brazilian and two security guards working at a diamond mine in Angola, an Australian partner in the Cuango mine said on Thursday.

The attack came on Wednesday afternoon about seven km (four miles) from the diamond mining town of Luzamba, Melbourne- based Ashton Mining said.

"They were killed in an ambush on their vehicle by an armed band believed to be UNITA (National Union for the Total Independence of Angola) rebels while traveling from the Tazua mining area to the project's operational headquarters at Luzamba in Lunda Norte Province," Ashton said in a statement, quoting from an "urgent communiquŽ" it received from the mine's owners.

"We are deeply saddened by the loss of life on the project," Ashton managing director Doug Bailey told Reuters. "No mine profit is worth the loss of life."

The company named the two foreign workers killed as mining manager Patrick Bergin, a Briton, and civil engineer Mario Trepechio of Brazil.

The killers were later pursued by members of the Angolan Armed Forces (FAA) stationed near the Cuango mine but Bailey said there had been no reports of any rebels being captured.

A heavily-armed private security force of 500 employed by the mine is patrolling the area to protect 120 foreigners working there, mostly Brazilian, and some 80 Angolan workers, he added. There are also five Britons remaining among the foreigners.

The mine is owned and operated by Sociedade de Desenvolvimento Mineiro de Angola SARL (SDM), which is one- third owned by Ashton.

Government officials in Angola have accused UNITA of acts of banditry aimed at destabilizing Angola's diamond-rich regions.

But Bailey said the attack in the northern region of the southern African nation known to diamond miners as Angola's "jewel box" because of its rich ore reserves, was unusual.

"It's normally been much more quiet where we are," Bailey said.

SDM gained access to the mine in January 1998 when UNITA rebels withdrew from the area.

In November, DiamondWorks Ltd of Canada said eight people were killed, including three foreigners, 16 injured and six abducted during an attack on another mine in northeast Angola, where attacks have been more frequent.

Employees of the Cuango mine are normally transported to work under armed escort during each daily shift change, although the four killed were traveling in a lone vehicle, Bailey said.

SDM was now reviewing its security at the mine, he added.

2 U.N. chartered C-130's like the one pictured here were shot down

Fighting between UNITA and the Angolan government erupted in early December, marking the collapse of a precarious four- year-old peace accord intended to end more than two decades of civil war in the southern African state.

Two United Nations-leased C-130 transport aircraft have been shot down in the past two weeks over central Huambo province, scene of fierce fighting between the government and UNITA rebels.

The Angolan government has pledged support in a search for the aircraft but said locating the aircraft would be difficult as hostilities showed few signs of abating.

Reuters contributed to this report.