Gunmen have killed seven United Nations peacekeepers and wounded 17 in an ambush in the Darfur region of western Sudan.

The incident, which occurred on Saturday, was the deadliest attack ever on the international force in the country.

The attack included sustained heavy fire from machine guns and possibly rocket-propelled grenades, targeting the force some 25 kilometers (15 miles) west of the town of Khor Abeche, UN forces spokesman Chris Cycmanick said.

Reinforcements later arrived to rescue the wounded, who included two female police advisers, the UN peacekeeping force said in a statement.

It wasn't immediately clear if any civilian personnel had accompanied the team into the ambush, Cycmanick said. He declined to announce the nationalities of those killed and wounded in the attack.

No group immediately claimed responsibility for the assault.

About 40 countries have contributed military personnel or police to the peacekeeping force.

A report issued by a UN panel of experts in February said that some armed opposition groups that are angry about the presence of peacekeepers have called the force "a legitimate target."

Peacekeepers have been targeted at various times since the international force began its work in the region in 2008. In the last fatal attack, gunmen shot and killed a Nigerian peacekeeper in April in East Darfur State. Before Saturday's attack, 150 people associated with the UN mission in Darfur had been killed while on duty in the region, according to the force's website.

The joint African Union-UN peacekeeping force, dubbed UNAMID, was established to protect civilians in Darfur, but also contributes to security for those providing humanitarian aid, verifying agreements, making political reconciliation efforts, and promoting human rights. It has about 16,500 troops and military observers and over 5,000 international police.

Darfur has been the scene of violence since 2003, when rebels took up arms against the government in Khartoum. There has also been tribal fighting in the region. More than 300,000 people have been killed in the conflict.

About 300,000 people have fled fighting throughout Darfur in the first five months of this year, according to the UN.

Over 100 UN peacekeepers were killed in 2012 while serving in the Darfur and Abyei regions of Sudan, the Democratic Republic of Congo, the Ivory Coast, and other countries. In addition, eight civilian contractors, such as pilots, also died on deployment with peacekeeping missions last year.