US election observers said Zimbabwe lacked a "tolerant democratic culture" in which citizens were allowed to vote freely. Picture: AP Photo/Wonder Mashura

Harare - US election observers said Zimbabwe lacked a "tolerant democratic culture" in which political parties were treated equally and citizens were allowed to vote freely.

The International Republican Institute and National Democratic Institute released their critical joint statement hours before President Emmerson Mnangagwa was due to take the oath of office on Sunday following Zimbabwe's July 30 election.

Mnangagwa will be sworn in on Sunday after the constitutional court on Friday confirmed his victory in a July 30 election.

Opposition leader Nelson Chamisa has rejected the ruling of the Constitutional Court that confirmed Mnangagwa as president after a vote that had been touted as a crucial step towards shedding Zimbabwe's pariah reputation and securing international donor funding to revive the economy.

Chamisa maintained that he had won the first election since the departure of Robert Mugabe last November and said the Constitutional Court had foiled his bid to subpoena the election commission to provide critical proof to bolster his case.

The US observers also said in their statement that Zimbabwe's security forces must refrain from use of excessive force during this politically sensitive period.