Europe's drug regulator said it is reviewing the "benefits and risks" of Novartis' multiple-sclerosis drug Gilenya and recommended that doctors closely monitor the hearts of patients after they are given the first dose of the drug.

The European Medicines Agency (EMA) said Friday that the review was prompted by reports of heart problems in patients taking Gilenya, as well as the November death of a 59-year-old patient in the US less than 24 hours after taking the first dose of the drug.

"The exact cause of this patient's death is still unexplained," the EMA said in a statement.

The US Food and Drug Administration (FDA) announced a safety review of Gilenya in December, also saying there was not a clear cause of the patient's death.

The EMA's review is expected to be complete by March. There is no time frame for the FDA's review.