FREETOWN (Reuters) - Sierra Leone is introducing new curfews for two northern districts after a spike in new Ebola cases to the highest level in months, President Ernest Bai Koroma said on Friday.

The 18-month-long Ebola epidemic has killed more than 11,100 people in West Africa, although weekly numbers of new cases have fallen sharply from last year's peaks. One of the three worst-affected countries, Liberia, was declared Ebola-free in May.

Sierra Leone and Guinea, however, are still regularly reporting several new cases daily, prompting both to extend emergency measures.

"I have instructed the security to institute chiefdom-level curfew and restriction on movement from 6 p.m. to 6 a.m. in Kambia and Port Loko districts, with immediate effect," Koroma said in a televised address.

Offenders will be detained and prosecuted if they violate the new measures, which will be in effect for the next 21 days. The two districts lie on the route between the capital Freetown and the Guinea border and have been the focus of recent cases.

Health workers say access is difficult in the maze of islands and creeks in the region, where dirt paths are often flooded in the current wet season.

Some residents are not complying with anti-Ebola measures and more than a dozen Ebola contacts have escaped quarantine, according to a report by the National Ebola Response Centre (NERC) in May.

"There will be night patrols, so the idea is to stop people from escaping using vehicles. If they run away on foot they can only get so far," said OB Sisay, a NERC official involved in "Operation Northern Push" for Port Loko and Kambia.

Oxfam's country director Thynn Thynn Hlaing warned that the new measures would only work if residents were involved in designing and implementing them.

There have also been breaches of anti-Ebola regulations in the capital. A member of parliament, Alie Badara Munu, was arrested for participating in a traditional burial in May.

Washing rituals for the dead can spread the virus, contained within body fluids such as blood and sweat.

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Sierra Leone reported seven confirmed cases on June 9, the highest count since March 24, according to the NERC.

But in many other districts of the small agricultural country of 6 million people, there are no more Ebola patients. Koroma said in his speech that restrictions on business opening hours would be eased in these areas.

(Reporting by Kemo Cham; additional reporting and writing by Emma Farge and Makini Brice; Editing by Mark Trevelyan)