Critics say the veteran leader has used the land reforms to help sustain his 28-year rule, rewarding supporters with fertile farms seized from whites -- although many are ill-equipped to properly engage in agriculture.

The official Herald newspaper quoted Mugabe as saying only 42 percent of the land was under full use and renewing threats to re-possess farms that were not being properly used in a country suffering food shortages and economic collapse.

"We would soon ask people who are not utilising their land to retire from the A2 (large-scale commercial) farms we allocated them," Mugabe told business leaders and government officials.

"There are people who took up land for status purposes and we want to advise them that they are not farmers, but settlers. We do not want settlers, we will get that land and give it to people who deserve it," he said.

Mugabe has previously threatened to reposess farms from those failing to produce. But critics question whether he would and point out that the government is still giving cheap fuel, seed and fertilisers to a few farmers from Zimbabwe's elite.

What was once southern Africa's breadbasket has been grappling with food shortages since 2001, worsening an economic meltdown that Mugabe's opponents blame on his policies. Zimbabwe's 165,000 percent inflation is the world's highest.

Mugabe says Western sanctions are responsible for the collapse.

The main opposition Movement for Democratic Change draws most of its support from urban Zimbabweans who have borne the brunt of the crisis, and its leader Morgan Tsvangirai beat Mugabe in a March 29 presidential election.

But official figures showed Tsvangirai did not win by sufficient votes to avoid a second round election, which has been set for June 27.

The MDC says ZANU-PF activists have killed 66 opposition supporters to try to intimidate voters before run-off, and police have detained Tsvangirai twice over the past week while trying to campaign. The ruling party blames the opposition for the political violence.

The party said its secretary general, Tendai Biti, was arrested on Thursday as he returned to the country after several weeks abroad.

Mugabe, in power since independence from Britain in 1980, dismisses the MDC as a puppet of Western powers seeking to oust him over the land redistribution programme.