Zimbabwe's foreign minister chastised U.S. Ambassador Christopher W. Dell on Wednesday but stopped short of expelling the envoy for giving two speeches last week in which he blamed the "corrupt rule" of President Robert Mugabe for the country's troubles.

Simbarashe Mumbengegwi, the foreign minister, warned Dell of the government's displeasure with his recent comments and reiterated threats that the envoy could be expelled if he made similar remarks again, according to news reports. A state radio broadcast said Dell had "deliberately gone on a confrontational course with the government."

On Tuesday, Mugabe was even more blunt. "You can tell him that I can't spell Dell, but I can spell hell," he told reporters in Harare, the capital, according to news reports. "That is what I know, and he might be there one of these days."

Timothy Smith, a spokesman for the U.S. Embassy in Harare, said Dell had no immediate response to the foreign minister's remarks but might reply after consulting with the State Department during an upcoming trip to Washington.

The clash has come at a volatile time in Zimbabwe. The leading opposition party, the Movement for Democratic Change, has split into feuding factions, and the country's labor union leaders have grown more aggressive in challenging Mugabe's 25-year rule.

Government-owned newspapers reported that more than 150 union activists, including top officials, were arrested Tuesday after protesting in Harare and the eastern city of Mutare, in violation of Zimbabwe's laws restricting political activity.

Morgan Tsvangirai, a former union head and leader of one of the splintered opposition factions, warned in a statement Wednesday that the arrests had brought Zimbabwe to "the precipice of a full-scale national conflict."

Dell, who became ambassador in August 2004, drew the ire of Mugabe on Oct. 10 by straying into a restricted area of a botanical garden near the presidential residence. Dell was briefly detained and later publicly accused by government officials of intentionally provoking a diplomatic incident. U.S. officials said the intrusion was a mistake caused by a lack of clear signs setting off the restricted zone.

Tensions escalated dramatically last week after Dell gave two speeches in which he accused Mugabe's government of causing Zimbabwe's economic collapse, chronic shortages of food and fuel, hyperinflation and an unemployment rate estimated at 70 percent.

"The Zimbabwe government's own gross mismanagement of the economy and its corrupt rule has brought on the crisis," Dell said, according to a transcript of the Nov. 2 speech provided by the U.S. Embassy.

Daily newspapers controlled by the government have relentlessly attacked Dell ever since, even suggesting that he was wandering in the botanical garden in search of sex.

In Washington on Monday, State Department spokesman J. Adam Ereli defended Dell and said his speeches last week "very fairly and accurately reflect the policy of the United States."