Late last month, the Bush administration announced a tightening of fiscal sanctions against the Sudanese government of Omar al-Bashir, which the United States holds responsible for genocidal actions in Sudan’s Darfur region. The White House also asked the Security Council to consider more robust international sanctions — including an arms embargo. Mr. Al-Bashir’s regime has so far largely ignored the United Nations, refusing to allow the full deployment of U.N. peacekeepers and blocking the delivery of humanitarian aid in Darfur.

Even in propositional form, the American and British push for sanctions was met with immediate opposition from Russia and China, Sudan’s major backers in the international arena. A more surprising opponent was South Africa, which assumed non–permanent membership in the Council this year. South Africa’s resistance to sanctions is at odds with its iconic status as a human rights success story, its claims to moral and political leadership on the African continent, and its participation in Darfur–related peacekeeping efforts. The South African claim that diplomacy is working is belied not only by the ongoing murder, rape, and expulsion of Darfur’s non–Baggara peoples, but also by Sudan’s intransigence vis-à-vis U.N. intervention.

South African opposition is especially remarkable given the importance of sanctions in the demise of the country’s apartheid regime. After the U.N. General Assembly revoked South Africa’s credentials and declared apartheid a “crime against humanity,” the Security Council mandated an arms embargo in 1977. Despite initial reluctance, by 1985 America and the European Community had placed costly economic sanctions on foreign investment, government loans, and a range of crucial goods. Without discounting the role of South Africa’s civic groups, these international sanctions were critical to the country’s achievement of majority rule.

Nevertheless, South Africa’s position on Sudan is woefully consistent with the country’s recent activity on the international stage. So far this year, South Africa has allied with Russia and China to thwart a Security Council resolution urging democratic reform in authoritarian Burma; nearly undermined the Council’s fragile compromise over placing sanctions on Iran; and failed once again to meaningfully condemn Robert Mugabe’s tyrannical regime in Zimbabwe.

Despite the disclaimers of South African diplomats, there is little doubting the government’s general opposition to supporting Western pressure on repressive regimes. This stance reflects two objectives of South African foreign policy: first, to consolidate its leadership position among African states; and second, to move the locus of international decision-making away from the West and toward emerging powers more representative of the developing world. Whatever the merits of these ambitions, it is clear that, to achieve them, the government is willing to forget the significance of external pressure in realizing a free and democratic South Africa. By opposing Western-led initiatives and siding with authoritarian, severely repressive, and militarily belligerent states, the South African government is helping to stymie the expansion of the same basic human rights it fought so long to achieve.

Consider the Burma vote, justified on procedural grounds: because the country’s military junta is not a threat to “international peace and security,” the resolution was more a matter for the U.N. Human Rights Council than the Security Council. However, no one outside Havana or Riyadh — both members of the body — believes the Human Rights Council to be even a half-effective advocate of the rights it is mandated to uphold. Asked about his reaction to the vote, Archbishop Desmond Tutu told reporters he was “deeply disappointed…. It is a betrayal of our own noble past.” Likewise South Africa’s opposition to military and financial sanctions on Iran. Recent events have revealed that Iran’s autocratic government is almost certainly pursuing a covert nuclear weapons program. South Africa’s opposition to the sanctions—supposedly motivated by concerns about restrictions on nuclear energy production—is bizarre for a country widely considered an exemplar of nuclear responsibility.

Closer to home, South Africa continues to coddle Mr. Mugabe’s dictatorial regime in Zimbabwe. Mr. Mugabe and his ZANU–PF party have overseen an evisceration of political and civil freedoms and the collapse of the country’s once vibrant economy; hundreds of thousands of Zimbabweans have fled to South Africa. Still, South Africa’s government has refused to seriously condemn Mr. Mugabe, an erstwhile hero of the struggle against white minority rule. In March, a widely publicized crackdown on oppositionists saw South Africa—in its most strongly worded statement to date—merely urge their ally to respect “the rule of law” and the “rights of all political parties.” However, South Africa later opposed bringing the Zimbabwe issue before the Security Council, and the government has shown no indication of supporting (even rhetorically) European Union and American sanctions on Mr. Mugabe’s regime.

And then there is Sudan. While the genocide charge is contested, Khartoum is certainly complicit in an ongoing and vicious campaign of ethnic cleansing; hundreds of thousands are dead and over 2 million are displaced. South Africa’s opposition to sanctions may score loyalty points with African states, but at a steep price: a freer hand for the perpetrators of yet another African crime against humanity, and the further betrayal of South Africa’s “noble past.”

Mr. Rosenberg is the Southern Africa analyst for Freedom House and a doctoral student of political science at the University of California, Berkeley.