Lusaka - Zambia's main opposition leader has given the speaker of parliament a seven-day ultimatum in which to declare vacant the seats of 16 of his party's MPs who were expelled, state radio reported Tuesday.

Most of the MPs from Michael Sata's Patriotic Front were expelled for defying a party directive not to take part in the National Constitutional Conference (NCC).

Once the seats are declared vacant, the southern African nation has three months within which to hold parliamentary by-elections under the current constitution.

In 2007, Sata's party opposed the formation of the NCC, a government-appointed body, heading the review of the constitution. (dpa)