Warning against any moves to carve up the Democratic Republic of the Congo, the US ambassador at the UN, Mr Richard Holbrooke, said foreign armies must not take advantage of the reported death of President Laurent Kabila.
As the United Nations refrained from commenting on Mr Kabila until his death was officially confirmed, Mr Holbrooke, in a previously scheduled address to African ambassadors, said foreigners had no role in the internal political process.
"It is essential that the foreign forces who have invaded and occupy large parts of the Congo halt their offensive action.
"They should not seek to take advantage of the events in Kinshasa to expand their presence. They should not play a role in the internal political process in Kinshasa," he added.
"The reported death of President Kabila may change the political landscape - indeed it will change the political landscape - but it will not alter the underlying reality," Mr Holbrooke said.
Rwanda and Uganda have troops in the Congo, backing rebels who tried to topple Mr Kabila. Zimbabwe, Namibia and Angola have sent troops to bolster the Congo's ragged army.
The UN Security Council, in a brief statement, only called on all parties to respect an often-broken ceasefire, refrain from military action and ensure the safety of UN personnel, which include over 100 in Kinshasa and an equal number in 13 other places around the vast country.
Behind closed doors, diplomats said Congo officials had told foreign embassies based in Kinshasa that Mr Kabila had been flown out of the country for medical treatment, despite numerous reliable reports he had been assassinated. The lack of official news also prevented the Secretary General, Mr Kofi Annan's office from issuing a statement it had prepared.
Some Western diplomats said they did not believe the bodyguard who shot Mr Kabila was acting on his own but rather on behalf of military or political officials frustrated at the stalemate in the civil war. "Kabila was neither winning the war nor moving forward with the peace," one envoy said after a closed-door council session.
The United Nations has been trying for more than a year to send a 5,537-member observer mission to the Congo to monitor a ceasefire agreement negotiated in Lusaka, Zambia, in mid1999 that called for withdrawal of all foreign troops. But Mr Annan has refrained from sending in a full UN force until fighting stopped.
Mr Holbrooke said every signatory had violated the Lusaka accord and all parties feared to reopen the pact because of concerns it might never be put back together again.
"Either the Lusaka agreement has to be implemented or it has to be restructured," Mr Holbrooke said. And whoever rules in Kinshasa has to undertake a dialogue with both the rebels and the unarmed opposition, which Mr Kabila has delayed, he said.