ABUJA (Reuters) - Nigerian President Muhammadu Buhari marked his return from medical leave in London with a rare appearance at a meeting on Thursday of the government's top advisory body.


Buhari attended a session of the National Economic Council, which is chaired by Vice President Yemi Osinbajo and whose members include state governors, the central bank governor and the finance minister. He does not usually attend NEC meetings.


Buhari returned on Friday from London, where he had been receiving medical treatment for seven weeks. His longer than expected absence and the fact that the nature of his illness was not disclosed had raised concerns over the 74-year-old's health.


Osinbajo has stressed that Buhari is ready to return to work. The president said on Friday he was feeling "much better" but wanted to rest over the weekend. His appearances since he landed have been restricted to the presidential offices and the State House.


At Thursday's NEC meeting, Buhari directed the central bank and finance ministry to release funds to the federal states to pay salaries of civil servants delayed due to a shortfall in oil revenues, the presidency said.


"One of these basic things is the issue of salaries. It is most important that workers are able to feed their families, pay rent and school fees, then other things can follow," Buhari told the meeting, according a presidency statement.

The combined debts of Nigeria's 36 states, including unpaid salaries, were around 658 billion naira ($2.15 billion) as of July 2015. The government loaned its states 90 billion naira in June 2016 in the most recent attempt to provide assistance.

The NEC also said Nigeria would offer a six-month window from May for tax defaulters to pay up in a bid to boost state revenues.

Nigeria could raise $1 billion from the scheme, according to a finance ministry presentation. "Tax payers will be allowed up to three years to settle their liabilities," the NEC said.

During Buhari's absence, when Osinbajo was acting president, the central bank devalued the naira for retail customers after the NEC called for an urgent review of the bank's foreign exchange policy.

Buhari has consistently opposed devaluing the naira since taking office in May 2015.

Journalists were asked to leave the NEC session before Buhari spoke.

(Reporting by Felix Onuah; Writing by Alexis Akwagyiram and Ulf Laessing; Editing by Alexander Smith and Giles Elgood)