A British nurse diagnosed with Ebola last month is recovering and is no longer in a critical condition, the London hospital treating her said in a statement on Monday.

Pauline Cafferkey, a 39-year-old nurse who normally works at a Scottish health center, became the first person to be diagnosed with the disease in Britain after contracting it in Sierra Leone where she was volunteering at an Ebola clinic.

"Pauline Cafferkey is showing signs of improvement and is no longer critically ill," the statement from the Royal Free Hospital said. "She remains in isolation as she receives specialist care for the Ebola virus."

Cafferkey is being treated with blood plasma from an Ebola survivor and an unnamed experimental anti-viral drug, the hospital has said.

The Royal Free, Britain's main center for Ebola cases, successfully treated British aid worker William Pooley with the experimental drug ZMapp -- a drug made by the small biotech company Mapp Biopharmaceutical in San Diego -- after he was flown back to Britain last August, suffering from the disease.

Supplies of ZMapp have since run out and none has been available to treat Cafferkey.