South Africa's ruling party is trying to rein in a young firebrand who is sowing discord among its old Communist allies, threatening President Jacob Zuma's efforts to build unity as the country grapples with economic recession.

Fearing the spat may get worse, the African National Congress on Tuesday rebuked Julius Malema, president of the ANC's Youth League, for his attacks against the South African Communist Party. ANC spokesman Jackson Mthembu said anyone who defies ANC orders not to fuel tensions must explain themselves in a disciplinary hearing.

Malema's actions have created a stir because the ANC Youth League, once led by Nelson Mandela long before he became president, is a powerful lobbying group within the ruling party and sees itself as king makers. The hostility has enthralled South Africans, earning banner headlines and prompting endless commentary and speculation on talk radio.

The infighting has put a strain on an alliance between the ANC, the SACP and the country's largest trade union federation that goes back decades, when the three banded together to fight apartheid. Since white rule ended with the country's first all-race elections in 1994, that unity has at times seemed forced. Under then President Thabo Mbeki, who succeeded Mandela, the alliance was battered by disagreements over the government's market-friendly economic policies.

Some observers say the latest tensions are a result of a succession battle that has already started over who will replace Zuma, who was inaugurated only last May. Malema is opposed to the growing influence of communists in the ANC and wants to keep its leaders from rising to power.

Matters came to a head last week when the 28-year-old Malema and some other ANC officials were booed at an SACP conference. After Malema retaliated by sending a threatening text message to SACP Deputy Secretary General Jeremy Cronin, who is also a member of the ANC's executive committee, the committee called for unity, asking that "members refrain from fueling tensions."

But Malema went on to tell the National Press Club on Tuesday that the heckling was an "invitation to war."

The hostility between Malema and the SACP broke into the open months ago after Malema began advocating that South Africa's mines be nationalized _ a policy even Cronin opposes for being unwieldy and expensive.

When Cronin, who also serves as the government's deputy transport minister, called Malema's ideas misguided, Malema retorted that he needed no advice from "a white messiah."

The infighting comes during a period when fewer tensions within the alliance had been expected.