HARARE - Zimbabwean police have blocked the launch of the main opposition party's election campaign set for Sunday in the latest clampdown on the president's main rival ahead of presidential and parliamentary polls in August, citing problems with the venue.

Nelson Chamisa, leader of the opposition Citizens Coalition for Change (CCC), has faced several hurdles on the campaign trail, with police banning a number of meetings in Zimbabwean cities and towns this week.

In a letter seen by Reuters on Friday, police said the opposition party could not conduct the rally in Bindura, 90 km (56 miles) north of the capital Harare, because the venue was not suitable for a gathering, citing lack of accessibility to water and sewer facilities.

"It provides a high security threat to participants," it said.

The Aug. 23 contest, expected to pit Chamisa against Zimbabwean President Emmerson Mnangagwa, 80, of the ZANU-PF party, comes amid a deep economic crisis, with high inflation and a currency that plunged more than 50% last month against the U.S. dollar.

The police letter ordered the opposition party to secure another venue and give it sufficient notice ahead of the rally.

CCC spokeswoman Fadzayi Mahere told Reuters that the party's lawyers were challenging the ban.

"While (the ruling party) ZANU-PF is capturing state institutions to ban our rallies, we are winning hearts and minds," Mahere said.

Political analysts say the general elections may fail the test of credibility if the clampdown on the opposition continues.

Mnangagwa is running for a second term in office.

(Reporting by Nyasha Chingono; Editing by Anait Miridzhanian, William Maclean)