WASHINGTON - Federal health officials on Friday approved a new type of morning-after contraceptive that works longer than the current leading drug on the market.

The pill ella from HRA Pharma reduces the chance of pregnancy up to five days after sex. Plan B, the most widely used emergency contraceptive pill, begins losing its ability to prevent pregnancy within three days of sex.

The Food and Drug Administration approved the drug Friday as a prescription-only birth control option. The ruling clears the way for U.S. sales of the drug, which is already approved in Europe.

Morristown, N.J.-based Watson Pharmaceuticals will market the drug in the U.S. under an agreement with HRA. Watson said it will launch the pill in the fourth quarter.

Studies of ella by its manufacturer showed the drug prevented pregnancies longer and more consistently than Plan B.

In a head-to-head trial between the two drugs, women who took ella had a 1.8 percent chance of becoming pregnant, while women who took Plan B had a 2.6 percent chance. Experts tracked nearly 1,700 women who randomly received one of the two pills within three to five days of having unprotected sex.

Plan B is made by Teva Pharmaceuticals and is also marketed in several generic versions. Unlike ella, Plan B and other generic versions are available without a prescription for women 17 years and older.

HRA Pharma did not request over-the-counter status for its drug.

Ella uses the hormone progesterone to delay ovulation, a key step in the fertilization process.

Despite this, the drug has drawn criticism from anti-abortion groups who say it is closer to an abortion pill than an emergency contraception pill.

Groups including the Family Research Council argue the drug is chemically similar to the abortion drug mifeprestone, which can be taken to end a pregnancy up to 50 days into the gestation period. That drug has been associated with severe infections and bleeding after abortion. However, FDA reviewers reported no life-threatening medical side effects with ella.

The most common side effects with the drug included headache, nausea and abdominal pain, according to an FDA release.

Abortion rights groups hailed the approval as an important step for the FDA, which was criticized in 2006 for its handling of Plan B's approval.

Last year a federal judge ruled that the FDA deliberately delayed making a decision on whether to permit over-the-counter sales of Plan B to teenage girls, at the behest of the Bush administration.

"Approval of ella is another indication that the FDA is committed to restoring scientific integrity in its decisions," said Kirsten Moore, president of the advocacy group Reproductive Health Technologies Project.

Privately held HRA Pharma is based in Paris and specializes in women's health products.