President Pasteur Bizimungu of Rwanda and Mr Kabila arrived in Zimbabwe for a hastily arranged meeting of seven regional heads of state to deal with the conflict in the former Zaire, now called the Republic of Congo.
Mr Kabila has accused Tutsi-dominated Rwanda of invading Congo to create a "Tutsi empire" and has promised to take the conflict to Rwanda. Rwanda and the Congolese Tutsi fighters, called Banyamulenge, backed Mr Kabila last year on his way to toppling dictator Mobutu Sese Seko, but have since grown disaffected.
The resurgence of conflict in Congo, and the prospect of renewed civil war in neighbouring Angola, has alarmed regional leaders. The fighting appears to threaten the spirit of peace that rose after apartheid's end in South Africa in 1994. As ouster of the corrupt Mobutu, Mr Kabila raised hopes for Congo's future. And after 20 years of civil war, Angola's warring factions had appeared to be ready to carry out a 1994 peace accord.
At a news conference in Lusaka, Zambia, on his way to Victoria Falls, Mr Bizimungu demanded that Mr Kabila justify his allegation that Rwanda was involved in the fighting.
"I understand that [Kabila] has declared war by arming 10 million people, so if we are provoked of course we will hit back," Mr Bizimungu said.
He said the leaders at the Victoria Falls summit would ask Mr Kabila to explain the current situation in his country and how the region could help.
Earlier yesterday, the Zimbabwean President, Robert Mugabe, ruled out military confrontation as a solution to the conflict in Congo.
Mr Mugabe said he "hopes the conflict does not escalate and cause political turmoil to the whole of the Southern African region and scare away investors".
The President added that he was confident the conflict would be resolved by the leaders, who planned to meet all day today.
Presidents Ben Mkapa of Tanzania, Sam Nujoma of Namibia and Frederick Chiluba of Zambia also arrived yesterday.
Uganda's President Yoweri Museveni was also due to arrive.
Noticeably absent was the South African President, Nelson Mandela. It was not clear whether he had been invited.