Five women have died after treatment with the abortion pill, raising fears about the risks of the medical method of terminating pregnancy used by more than 50,000 women a year in England.

Four of the deaths were in the United States; all were young healthy women who had successful terminations and then developed fatal infections within a few days that progressed rapidly, causing septic shock. The fifth death was in Canada.

The US Food and Drug Administration issued a "Black Box" warning last July, alerting doctors to the deaths - details of which are published in the New England Journal of Medicine - and warning of the risks.

The abortion pill is widely used in the UK but no similar warning has been issued here. A spokeswoman for the Medicines and Healthcare Products Regulatory Agency said it had reviewed the US evidence with other European regulators and concluded that "no new safety issues had arisen".

The American women were aged 18, 21, 22 and 34. Three died within hours of being admitted to hospital and the fourth was dead before medical help reached her. All five deaths have occurred since 2001.

In England, the abortion pill is used in one-third of the 185,000 annual terminations. It is given in two stages - an oral dose of mifepristone (also known as RU486) and a second drug, a prostaglandin called misoprostol, which is inserted into the vagina and causes the uterus to contract, expelling its contents. In the UK, gemeprost is used in place of misoprostol.

The abortion pill is only used in early pregnancy up to nine weeks in the UK (seven in the US) and is regarded as safe.

Investigation of the American deaths showed that all were infected with a bacterium, Clostridium sordellii, which exists naturally in the genital tract but in rare cases can cause toxic shock syndrome after childbirth.