Zimbabwe Prime Minister Robert Mugabe denied today that he had ordered opposition leader Joshua Nkomo killed, and said Nkomo is "welcome" to return from exile any time to his home where he can live in safety.

"I assure you that I'm no assassin. What will I gain by having him killed? If anything, it would make him more of a martyr than he already is," Mugabe said.

Mugabe said he was aware of reports that Nkomo's wife and children had been arrested after the opposition leader fled to Botswana Tuesday, but that he had no details of what prompted the arrests.

"I believe that those who arrested her and some members of the family had reasons. I assure you, no one will be arrested without reasons," Mugabe said at a press conference during the nonaligned nations summit here.

In Harare, the Zimbabwe capital, Home Affairs Minister Herbert Ushewokunze said Mrs. Nkomo had been freed Thursday "on humanitarian grounds." Nkomo's son, daughter and son-in-law were still being held, he said.

Information Minister Nathan Shamuyarira said Zimbabwe was "taking up the question of Joshua Nkomo's entry and stay in Botswana and the issue of cross-border violations generally with the Botswana government through normal diplomatic channels," Associated Press reported.

Mugabe said his information was that Nkomo, whom Mugabe removed from the Cabinet in February 1982 and accused of plotting a coup, had left Zimbabwe "temporarily, during which time he hopes to work on what he calls ways to resolve the problems of our country." He added, "I haven't caused him to flee. He is welcome back home."

Before crossing into Botswana, Nkomo said at an early morning clandestine press conference Sunday that troops sent by Mugabe to search his home in Bulawayo would have killed him if he had been there. Nkomo's chauffeur was shot and killed in the encounter. Today's denial was Mugabe's first statement since Nkomo fled the country.

Nkomo was placed under virtual house arrest last week in his native Matabeleland province in western Zimbabwe after accusing Mugabe's troops of killing scores of civilians in the province. Last month, Nkomo was arrested briefly as he was about to board a plane to South Africa.

Mugabe accused Nkomo of being in "collusion" with South Africa to destabilize Zimbabwe by forming a "Matabeleland brigade" to stir up dissidents among Nkomo's fellow Ndebele tribesmen in the province. Mugabe, who is from the dominant Shona tribe, sent the North Korean-trained 5th Brigade to Matabeleland in January to crush the dissident movement, and church and relief officials have estimated that more than 1,000 civilians have been killed in the campaign.

When asked if Nkomo had betrayed Zimbabwe, Mugabe said that Nkomo wanted to leave the country to meet with South African officials, and that dissidents have also been going to South Africa for guerrilla training. "So we accused him of collusion with South Africa."

Asked if he would stick to his insistence on one-party rule in Zimbabwe, Mugabe said, "Yes, yes, yes! Three yeses, on the basis of asking the people if they agree with us on establishing democratic one-party rule, and I'm sure the answer will be yes."

He said a one-party state is "not necessarily a dictatorship because a multi-party state can be dictatorial." He said the one-party system would be "as accommodating as possible," and that he would attempt to include elements from other parties in the single party.