LISBON, Portugal (AP) _ Angola's Defense Ministry said Monday that South African troops have taken up positions inside Angola to support rebels fighting the Angolan government and have killed at least 53 soldiers.

Condemning the incursion, the ministry charged in a statement that South Africa was seeking to ''multiply conflicts'' in southern Africa. The statement was carried by the state-run Angolan news agency ANGOP, monitored in Lisbon.

On Thursday, South Africans attacked Angolan troops near the town of Xangongo in Cunene province, about 100 miles north of the border with South- West Africa, the statement said. Fifty-three Angolan soldiers were killed.

South African troops have repeatedly entered southern Angola since it became independent from Portugal in 1975.

South Africa has said its troops only enter Angola to pursue SWAPO guerrillas based in southern Angola. SWAPO, or South-West Africa People's Organization, has fought since 1966 to end South African control of the desert territory of South-West Africa, also known as Namibia.

South Africa has also denied that its troops inside Angola provide battle support for UNITA, the rebel group fighting Angola's Marxist government. South Africa has acknowledged, however, that it gives other aid to UNITA, or the National Union for the Total Independence of Angola.

The Defense Ministry statement said the first South African troops were spotted in early May. Since then, hundreds of soldiers have crossed over the border with South-West Africa into Angola's Cunene province to support UNITA rebel positions, the statement said.

On May 6, six South African helicopters stafed Cunene town, the statement said. On May 10, a South African armored convoy of 67 vehicles took up positions in the Buabua region, about 47 miles away from Cunene capital of Ngiva, the statement said. On May 13, South African forces overran the town of Iona and the next day, two battalions were sighted in the town of Evale, the statement said.

The Angolan statement said that on May 16, helicopters dropped troops in the town of Virei and other soldiers were sighted outside Donguena and Nainana-Calueque on May 19.