Uganda's main opposition party says more than 200 of its supporters have been detained across the country following a disputed election.

Yusuf Nsibambi, a lawyer for the Forum for Democratic Change, said Friday that the party faces a crisis as it prepares to launch a legal challenge against the victory of long-time President Yoweri Museveni.

Nsibambi said most of those in detention are opposition party representatives who carried crucial polling material that could be used as evidence in a possible court case.

Opposition leader Kizza Besigye himself has been under house arrest since last Friday. He has rejected the official election result as fraudulent.

A police spokeswoman, Polly Namaye, said there are several ongoing operations against suspected criminals in different parts of Uganda but denied opposition supporters are being targeted.