MONROVIA (Reuters) - A Liberian woman has died of Ebola in a hospital in Monrovia shortly after being admitted, becoming the sixth confirmed case of the virus since it resurfaced last month after a seven-week lull, a senior medical official said on Tuesday.

The victim from Montserrado County, which contains Monrovia, is thought to be linked to the other five cases from neighboring Margibi County, where the disease reemerged.

Her detection raised fears that the infection may be spreading in a new area of the country.

"There is one new case. This time, the response area is Montserrado county. The person died in Monrovia," Liberia's Chief Medical Officer Dr. Francis Ketteh told Reuters.

A health report sent to officials in the anti-Ebola response said that the woman died a few hours after admission, indicating that surveillance of known contacts from the earlier cases had not been rigorous enough.

More than 11,200 people have died from Ebola since the epidemic began in December 2013. Liberia was declared Ebola-free on May 9 but reported a new case nearly two months later.

Health officials say the virus probably remained latent in the country during that period and could have been reactivated by a survivor, via sexual transmission.

(Reporting by Alphonso Toweh and Emma Farge; Editing by Daniel Flynn)