Harvard University should follow the University of California and other schools by giving up more investments in stocks linked to Sudan, where the government has been implicated in acts of genocide, a student group said.

Harvard Darfur Action Group will ask the university to more closely monitor its investments for stocks such as Chinese oil companies PetroChina Co. and Sinopec, said Rebecca Hamilton, a student at Harvard Law School and the Kennedy School of Government in Cambridge, Mass.

The call for tighter monitoring to target stocks of the "worst offenders" follows reports that Harvard still holds about $16 million in PetroChina and Sinopec after pledging in the last two years to divest. In March, the University of California voted to drop direct and indirect holdings in nine companies with Sudan ties, including the two oil companies.

"It is in Harvard's interest to find a permanent solution, rather than risk having their good reputation on this issue called into question," Ms. Hamilton, co-founder of the student group, said in an e-mail.

Harvard, the world's richest university with a $29.2 billion endowment, holds shares in index funds that invest in PetroChina, Sinopec and other companies that do business in Sudan.

Government-supported militiamen have attacked villages in Darfur, in western Sudan, for four years, killing as many as 400,000 people and displacing 2 million others. The U.S. State Department and Congress in 2004 labeled the campaign genocide.

University spokesman John Longbrake said it's Harvard's policy not to discuss individual investments. Mohamed El-Erian, chief executive officer of Harvard Management Co., the university-affiliated firm that invests the endowment, didn't respond to telephone and e-mail messages seeking comment.

The universities of California, Vermont and Washington are among 30 higher-education institutions that have chosen to divest, said Daniel Millenson, president and national advocacy director of the Sudan Divestment Task Force. Two dozen more schools are weighing divestment, as are 20 state legislatures, said Mr. Millenson, a sophomore at Brandeis University in Waltham, Mass.

Harvard is in a "complicated investment morass," said Tim Smith, a senior vice president at Walden Asset Management, a $1.5 billion investment firm in Boston.

"What isn't acceptable for them is to just sit on their hands," said Mr. Smith, president of the Social Investment Forum trade association, which represents mutual funds and other investors. "You have to find some way to address the issue."

Harvard Corp., the university's governing board, in April 2005 ordered the sale of PetroChina stock, saying revenue from the firm's partnership with Sudan's government helped finance the attacks. In March, President Lawrence Summers, who has since resigned, said Harvard would sell its shares in Sinopec, also called China Petroleum & Chemical Corp., a move demanded by 1,200 students, faculty and alumni who signed an online petition.

As of Sept. 30, Harvard owned the PetroChina and Sinopec interests through exchange-traded funds operated by Barclays Global Investors, a San Francisco-based unit of Barclays Plc. Harvard didn't directly hold the shares.

Acting President Derek Bok told the student-run Harvard Crimson newspaper in an e-mail Jan. 7 that the investments must have occurred before he took the job in July and that he didn't know about them.

Mr. El-Erian joined Harvard Management full time in February after a large segment of the endowment switched into index-tracking investments such as Barclays' iShares funds.

Harvard appears to hold more in Sudan-linked companies than in 2004, when its $3.9 million investment in PetroChina prompted a student-led divestiture campaign.

The university owned 4.6 million shares of the iShares MSCI Emerging Markets Index fund as of Sept. 30. The iShares fund was the university's largest publicly disclosed holding. The shares, if still held Jan. 11, would have been worth $503.6 million. PetroChina and Sinopec shares represented about 1.8 percent of the fund, valuing Harvard's stake at about $9.1 million.