Despite evidence that a group of experimental blood substitutes nearly tripled the risk of heart attacks and caused a 30% increase in deaths, the Food and Drug Administration continued to approve some clinical trials of the products, researchers said yesterday.

Although no such trials are proceeding in America, the agency should have known about the risks by 2000 and halted all trials, thereby preventing deaths that have occurred in the past seven years, according to a report published online by the Journal of the American Medical Association.

Had the agency reported publicly what it knew then, ongoing trials in eight other countries probably would have been blocked, the researchers said.

The director of FDA’s Office of Blood Research and Review, Dr. Jay Epstein, countered in a news conference that the agency weighed the risks and benefits of each proposed study and blocked some and allowed others to proceed.

He added that the FDA has been “highly vigilant in its oversight” and that it also has concerns about the safety of the products, which is why, he said, “There are no ongoing studies of blood substitutes in the U.S. and no approved products.”

The FDA has convened a two-day meeting on the future course of the products beginning today.

The latest findings, however, deal a setback for the long-sought goal of developing artificial blood, which has been spearheaded by a handful of small companies.