Zambian authorities closed the country's top courts on Monday, blocking access to the premises on the last day that the opposition could file a challenge to this month's disputed election.

A memorandum from the chief administrator of the judiciary, which was seen by Reuters, said that "for security reasons, all members of staff are advised not to report for work today".

Police spokesperson Godfrey Chilabi told Reuters that security assessments were ongoing, and declined to give details. A spokesperson for the judiciary could not be reached.

Opposition leader Brian Mundubile said last week that he was planning to file a petition at the Constitutional Court to challenge the results of an August 13 election in which he came second to President Hakainde Hichilema.

The deadline to file such a challenge is seven days after the result was announced, which would be in the early hours of Tuesday.

OPPOSITION STILL AIMING TO FILE PETITION

At the Supreme Court premises in Lusaka, which also includes the Constitutional Court, all of the gates were closed and police could be seen inside.

Hichilema won re-election with about 60% of votes in the Southern African copper producer, but two reports by independent observers found indications the that Hichilema's vote count was inflated. Hichilema has denied any fraud.

Following the arrests of several of his associates, Mundubile was summoned by police for questioning last week in connection with alleged national security threats, which he says are fabricated.

Analysts and human rights lawyers said they suspected he might be prevented from filing his petition, though Hichilema's party said that Mundubile was free to use the legal routes available to him.

"We are trying our best to ensure that the petition is filed but we will see how it goes," said New Heritage Party President Chishala Kateka, whose party belongs to Mundubile's opposition alliance.