The Gambia's security forces have taken over the headquarters of the electoral commission, its chairman says, as the country's president refuses to accept his loss in recent elections.

Alieu Momar Njai told the BBC that staff were barred from entering.

President Yahya Jammeh initially conceded defeat to Adama Barrow in a recent poll, before changing his mind.

Visiting West African leaders have met Mr Jammeh to try to persuade him to step down after 22 years in power.

"We hope and pray that he [Jammeh] accepts their advice and leaves office," Mr Njai said.

The head of regional bloc Ecowas, Marcel de Souza, would not rule out sending in troops.

"We have done it in the past," he told Radio France Internationale.

"We currently have troops in Guinea-Bissau with the Ecomib mission. We have had troops in Mali. And therefore it is a possible solution."

Mr Jammeh has questioned the validity of the count after the electoral commission changed some results, even though it insists the outcome was not affected.

The commission said Mr Barrow obtained 222,708 votes (43.3%) compared with Mr Jammeh's 208,487 (39.6%). A third candidate, Mama Kandeh, won 89,768 votes (17.1%).