Mwanawasa is facing a united challenge

The United Democratic Alliance (UDA), formed five months ago, says it will be represented by a single candidate in each of the 150 constituencies.

Last week, the UDA chose businessman Hakainde Hichilema, as a joint candidate to contest the presidential election being held the same day.

He will challenge Levy Mwanawasa, who is seeking a second five-year term.

The BBC's Musonda Chibamba in the capital, Lusaka, says this is the first time in more than 35 years that political parties in Zambia have come together in this way.

A preliminary nominations list released earlier this week suggest that a total of 11 candidates will contest the presidency on 28 September.

Mr Mwanawasa was elected in 2001, and said in April that he would stand for a second term despite suffering a minor stroke.