Stanford University announced Thursday that it would sell its holdings in four companies -- PetroChina, ABB Ltd., Sinopec and Tatneft -- that conduct business in Sudan that has the effect of supporting the government there.

University officials cited the government's complicity in genocide in the region of Darfur in explaining the decision.

Student groups for years have urged universities to use divestment policies to take stands on international issues. In the 1980s, many colleges sold holdings in companies that did business in apartheid-era South Africa. But then and today, many trustees and endowment managers have resisted the idea of linking college investment policies with issues of social justice, however worthy they may be.

The push on investments in Sudan is relatively recent, and Stanford's move may well give it momentum. In April, Harvard University sold holdings in PetroChina, and pro-divestment activists wanted a prominent West coast institution to follow suit.

In announcing their decisions, officials at both Stanford and Harvard stressed that they would support divestment only in rare situations.

"Divestment is an act that should be made rarely and carefully," said John L. Hennessy, Stanford's president, in a statement. “In this case, it was clear that the genocide occurring in Darfur, which appears to be at least partly enabled by these four companies, is in direct opposition to Stanford University’s principles.”

When Harvard sold its holdings in PetroChina, a statement from the Harvard Corporation noted that the university "maintains a strong presumption against the divestment of stock for reasons unrelated to investment purposes."

Last month, the International Crisis Group sent a letter to 100 universities urging them to follow Harvard's lead.

Student groups are also mobilizing over the issue. Students Taking Action Now: Darfur, known as STAND, was founded in September and currently has 80 campus chapters. The group is planning a major push on divestment in the next academic year.