Ministers from the regional political bloc, Ecowas (Economic Community of West African States), led by Cheik Tidiane Gadio, the Senegalese foreign minister, were also meeting with Guinea-Bissau officials.
Schools, ministries and businesses, meanwhile, reopened in the capital, Bissau, on Tuesday after soldiers largely withdrew from the streets.
Vieira was killed by members of the army while fleeing his presidential home, hours after a bomb killed Tagme Na Waie, the army chief.
"He was savagely beaten before being finished off with several bullets"
Doctor who carried out autopsy on Vieira
Vieira, who had endured tense relations with the military, had escaped a previous attempt on his life last November.
The doctor who carried out an autopsy on Vieira's body said the head of state was savagely beaten before being shot several times in the throat and face.
"The president was hit by several bullets in the thorax and face and his body shows the marks of violent blows.
"He was savagely beaten before being finished off with several bullets," the doctor said.
Guinea-Bissau has a history of coups and has become a notorious transit point for the cocaine trade between South America and Europe, raising the stakes in long-running power feuds between political and military leaders.
|A bomb, placed under a stairway leading to his office, killed General Na Waie [AFP]
The African Union's Peace and Security Council, meeting in an emergency session in Addis Ababa on Tuesday, demanded a probe into the killing of Vieira.
According to the AU's statutes, member states should be suspended in the event of an unconstitutional power change, as were Mauritania and Guinea Conakry following coups last year.
Details have started to emerge about the military assault on the president's home on Monday.
A soldier, who said he took part in the operation, said the troops who killed the president left Mansoa barracks, 60km north of Bissau, late on Sunday, to "liquidate President Vieira".
He said they left Mansoa shortly after the announcement of the death of the armed forces chief of staff.
Before reaching the president, the unit forced the release of seven soldiers from a police station in the capital, where they had been held since the November 24 attack on Vieira's residence, in which two of his guards were killed.
Relations between the president and Na Waie had reportedly deteriorated drastically after that attack.