Gambia's embattled dictator despatched riot police to occupy the country's electoral commission on Tuesday as he defied mounting international pressure to step down.

Security forces loyal to President Yahya Jammeh, who suffered a shock defeat in elections on December 1, surrounded the commission's offices and barred anyone from entering, staff said.

The move appeared to be linked to Mr Jammeh's unexpected announcement on Saturday that he planned a legal challenge to the election results, which he had previously said he would abide by.

Critics suspect the former army officer is planning a coup.

The move came as three West African presidents led a heavyweight delegation to Gambia to persuade Mr Jammeh to stick to his original promise to go quietly.