Zambia will hold presidential and parliamentary elections on Aug. 11 under a new constitution, a government spokesman said on Monday.

The elections are expected to be tight contest between President Edgar Lungu's ruling Patriotic Front (PF) party and Hakainde Hichilema's opposition United Party for National Development (UPND).

Lungu is expected to assent to the constitutional amendments on Tuesday, ratifying the election date, his spokesman Amos Chanda said.

Under the previous constitution, the president set the election date every five years.

Other amendments include a clause requiring a winning presidential candidate to get more than 50 percent of the valid votes cast, he said.

Presidential candidates will run on a joint ticket with a vice-presidential candidate, unlike the present situation where the president appoints his deputy, Chanda said.