TOKYO (AFP) - Officially pacifist Japan will waive its customary restrictions on arms exports to supply ammunition to South Korean peacekeepers in South Sudan, where fierce fighting has broken out, reports said on Monday.

Japanese peacekeepers engaged in non-combat operations in the African country will provide 10,000 rounds of ammunition to the South Koreans there, the reports said.

It will be the first time for Japan, which is barred by its post-World War II pacifist constitution from using force to settle disputes, to provide weapons to the military of another country through the United Nations, the Jiji and Kyodo news agencies said.

They said the decision was made at an emergency meeting on Monday of Japan's National Security Council chaired by Prime Minister Shinzo Abe, in response to a South Korean request.

Fighting has spread across South Sudan since December 15, after President Salva Kiir accused his former deputy Riek Machar of attempting a coup. Machar denied the claim and accused Kiir of carrying out a vicious purge of his rivals.

The Japanese law governing peacekeeping operations says it can provide such supplies, with cabinet approval, as part of its cooperation in UN activities.

About 350 Japanese troops are deployed in South Sudan in operations such as construction and maintaining infrastructure, the TV Asahi network said.

South Korea asked the UN Missions in South Sudan for extra ammunition since its troops are mostly engineers and medics and fears of civil war have grown, the South's Yonhap news agency reported.

Citing the defence ministry, it said the 280-member South Korean contingency operates from the town of Bor, 170 kilometres north of the capital Juba.