Fifteen opposition politicians in Zimbabwe have filed an appeal in court challenging a decision by the parliamentary speaker to declare their seats vacant.

Speaker Jacob Mudenda had received a letter - full of grammar mistakes - from a man falsely claiming to be the secretary general for the main opposition party, Citizens Coalition for Change (CCC). The letter said that 15 of the CCC's MPs were no longer party members.

CCC leader Nelson Chamisa had asked the speaker to disregard the letter, saying the party has no secretary general.

Despite Mr Chamisa's request, Mr Mudenda declared the 15 seats vacant on Monday.

The move has paved the way for by-elections that could hand the ruling Zanu-PF party, which won a disputed election in August, a two-thirds majority needed to amend the constitution.