imbabwe today detained opposition leader Joshua Nkomo for eight hours and prevented him from leaving the country in a move that is bound to exacerbate political tensions in the embattled southern African nation.

Nkomo said in a telephone interview from his home in Bulawayo that he was arrested at the city's airport as he was about to board a flight for South Africa en route to an international conference in Prague, Czechoslovakia.

He said the police gave no reason for the arrest, which he called "unbelievable." A government official, however, said Nkomo was detained because he "has certain charges to answer."

After being held for two hours at the airport, he was taken to a police station in a suburb of Bulawayo, the southwestern Zimbabwean city that is Nkomo's tribal stronghold.

Nkomo's detention is the harshest action taken toward him by the government in the year since Prime Minister Robert Mugabe fired his former guerrilla ally from the Cabinet. Nkomo and Mugabe each led separate but allied guerrilla forces in the war to achieve black-majority rule in the former British colony then known as Rhodesia.

But after they helped form a government in 1980, rivalries developed again between the two leading to Nkomo's ouster from the Cabinet. Mugabe accused Nkomo of stashing weapons for a planned coup--a charge Nkomo denied--but until today he had taken no legal action against Nkomo.

Nonetheless, tensions have grown in the area around Bulawayo, and Mugabe has sent an elite Army brigade to the area to bring the Nkomo supporters under control.

During his eight hours in detention at the police station, Nkomo said police searched his body and luggage but gave him no reason for the arrest. He said they acknowledged they did not know why they had been ordered to pick him up.

Eyewitnesses at the airport said Nkomo became furious when two police officers prevented him from boarding the plane after he had cleared customs and immigration.

"Why are you doing this to me? What have I done wrong?" he shouted, according to news service reports.

Three of Nkomo's aides who were to accompany him to the World Peace Council in Prague also were arrested, and they are still being held, Nkomo said.

In the past months Matabeleland, the southwestern area where Nkomo's Ndebele tribe has a majority, has been subjected to harsh military repression as the government has sought to wipe out dissidents that it says are loyal to Nkomo. The government accuses the dissidents of killing at least 120 people in the past year.

Nkomo accused soldiers of killing at least 95 civilians in the area in the past month. People who have fled the countryside for Bulawayo have claimed that the toll may be much higher as the troops reportedly have gone on a rampage of killing, raping and looting.

The government linked today's arrest to the current treason trial of Nkomo's top two military aides during the guerrilla war, Dumiso Dabengwa and Gen. Lookout Masuku.

"In view of the trial and the incriminating evidence we are getting, the government would not be happy to have him leave the country," Justin Nyoka, the spokesman, said. "We think he has certain charges to answer."

Nkomo, however, denied the claim and said the police did not mention the trial in their interrogation. He was allowed access to a lawyer, but his wife was only permitted to see him just before his release, Nkomo said.

The leader of the Zimbabwe African People's Union said police had kept his passport and airline tickets, thus preventing him from leaving the country. He said he demanded their return but the police maintained they had to refer the matter to higher authorities.

He called his detention "terrible" and said even the white government of former prime minister Ian Smith, which detained him for 10 years, had never prevented him from traveling in such a manner. Last year, the government seized Smith's passport after he made critical remarks in the United States.

Nkomo said he still hopes to leave soon for the meeting of the World Peace Council, where he holds a position as a vice president.

The dissident violence began after the arrest of Dabengwa and Masuku last March, reaching a peak in July when six foreign tourists, including two Americans, were kidnaped. The dissidents demanded the release of Dabengwa, Masuku and others, but the government had refused to deal with them. The fate of the hostages is still unknown.

There was a new spate of violence at Christmas that led Mugabe to station the North Korean-trained Fifth Brigade in Matabeleland to crush the dissidents. Since then the bloodshed has increased dramatically as the 5,000-man force is dominated by Mugabe's Shona tribe, the archrivals of Nkomo's Ndebeles.

Mugabe said Thursday that the Fifth Brigade "would not leave Matabeleland until every dissident had been routed," according to The Herald, the country's main newspaper. He said his party had "won the country through the barrel of the gun and it will use the gun to destroy the dissidents," who he charged were trying to put Nkomo in power.

"Who do they think they are?" Mugabe asked. "Who does Nkomo think he is?"

Mugabe gave his own answer to that question the next day in a political rally in eastern Zimbabwe, his political stronghold. He accused Nkomo of being "a puppet" and "a yes-man" of white-ruled South Africa which, the prime minister charged, was using Nkomo "to destroy the independence of Zimbabwe."

Meanwhile, Information Minister Nathan Shamuyarira announced that the government had revoked the press accreditation of Newsweek correspondent Holger Jensen "because of persistent false and exaggerated reports on Zimbabwe since independence."

In a report from Matabeleland in this week's Newsweek, Jensen gave details of alleged massacres and said 500 people were killed in the past three weeks. Shamuyarira said he spent two days in Bulawayo checking on the reports and called them "utterly false."

Jensen is the second correspondent to be barred from reporting in Zimbabwe since independence. Many more were banned during Smith's rule.