HARARE, Dec 6 (Reuters) - Zimbabwe’s central bank sacked executives at four banks accused of illegal foreign currency trading, state media reported on Saturday, as international criticism of President Robert Mugabe’s government increased.

British Prime Minister Gordon Brown added his voice to condemnation of Mugabe, saying the world should tell the 84-year-old ruler “enough is enough”. He urged coordinated international action to help Zimbabwe overcome food shortages and a cholera epidemic.

The southern African nation, isolated by Western countries under Mugabe’s authoritarian rule, is on the verge of collapse. Food stocks are running out, official inflation is at 231 million percent and a cholera outbreak has killed 575 people and sickened almost 13,000.

The Reserve Bank of Zimbabwe has been unable to print money fast enough to keep up with soaring prices, which double every 24 hours, and has tried to stamp out a thriving black market for U.S. dollars and other foreign currencies.

This week it dismissed the chief executives and senior managers at four banks, state media reported, saying they diverted large sums of Zimbabwean dollars to the black market before the notes were introduced.

“This is criminal because the money was not yet legal tender when it was released,” central bank Governor Gideon Gono was quoted as saying in the Herald newspaper, adding the executives faced prosecution.

Refering to past media reports that suggested the central bank itself had in the past purchased foreign currency from the black market, Gono said: “We are sick and tired of being labelled crooks.”

CLASHES

Zimbabweans have grown increasingly angry over the government’s failure to tackle the crisis. Many are forced to line up outside banks for hours to try to get scarce banknotes, often coming away with barely enough to buy a loaf of bread.

Tensions flared in the capital Harare last week when mobs and police clashed with groups of unarmed soldiers who had seized cash from foreign currency traders and shops. Trade union activists also took to the streets to protest against the crisis.

The central bank said it would soon introduce a Z$200 million note (worth $20 on the black market) after launching Z$10 million, Z$50 million and Z$100 million notes on Thursday.

The economic meltdown has led to the crumbling of basic services, including health care and water treatment facilities.

Cholera has spread to neighbouring South Africa, Mozambique, Zambia and Botswana and forced Mugabe’s government to declare a national emergency and appeal for international assistance.

Western nations as well as Zimbabwe’s neighbours in Africa have pledged humanitarian assistance, while sharpening their criticism of Mugabe’s government and his failure to establish a unity government with the opposition MDC.

U.S. Secretary of State Condoleezza Rice said on Friday it was time for Mugabe to step down, echoing a call on Thursday by Nobel laureate and South African Archbishop Desmond Tutu.

In a further sign of growing international pressure, the European Union is considering applying more sanctions against Zimbabwe next week unless progress is made in ending a political deadlock over how to implement the Sept. 15 power-sharing deal.

Mugabe and MDC leader Morgan Tsvangirai have deadlocked over the control of ministries in the unity government. Negotiators from Mugabe’s ZANU-PF party and the MDC are scheduled to meet again with South African mediators in two weeks. (Additional reporting by Kate Kelland in London; Editing by Paul Simao and Janet Lawrence)