African Union leaders are meeting to discuss the conflict in Mali, as members move to deploy troops to help the French-led operation there.
African states have pledged 7,700 troops to support French and Malian forces in their campaign against Islamist militants in northern Mali.
Only a small part of the African force has so far deployed.
French-led troops have retaken several towns since France intervened two weeks ago, and on Saturday captured Gao.
The French defence ministry said troops gained control of the city - northern Mali's most populous - after securing the airport and a strategic bridge to the south.
Most militants appear to have fled into desert hide-outs and the hunt for them may prove more difficult once all major towns are secure, says the BBC's Thomas Fessy in the capital, Bamako.
Gao's mayor, who had been ousted when Islamists seized control of northern Mali last year, returned to the town on Saturday.
The other major northern cities, Kidal and Timbuktu, remain in Islamist hands. French forces are now moving towards targeting Timbuktu.
African leaders are meeting in the Ethiopian capital, Addis Ababa, on the opening day of an African Union summit.
The BBC's James Copnall in Addis Ababa says that so far, the continent appears to be speaking with one voice on Mali, and the hope is that more African states will send troops.
The summit will also consider who is going to pick up the bill for what is already a very costly operation, he adds.
A number of West African countries on Saturday raised the total number of troops pledged to 5,700. Separately, Chad has said it will send 2,200 soldiers.
AU leaders have already called on the UN Security Council to authorise immediate logistical help that would allow African troops to deploy more rapidly.
Some 3,700 French troops are engaged in Operation Serval, 2,500 of them on Malian soil.
Meanwhile, the US said it would provide mid-air refuelling for French warplanes.
The Pentagon said it had also discussed plans for the US to transport troops to Mali from countries including Chad and Togo.
Islamists seized a vast area of northern Mali last year and have tried to impose strict Sharia, or Islamic law, on its inhabitants.
France intervened militarily as the Islamists advanced further south. It said that the capital, Bamako, was under threat.
As French and Malian troops moved into Gao, Malian officials spoke of scenes of joy, but also some looting.
"Possibly at a certain point the enemy in front of us was underestimated," Malian Foreign Minister Tieman Coulibaly said ahead of the summit in Addis Ababa.
"But everyone has seen that this terrorist group intends to spread its criminal purpose over the whole of Mali, and eventually target other countries."
The AU has recommended civilian observers monitor the human rights situation in the areas which have come back under the control of the Malian government.
Human rights groups have accused the Malian army of committing serious abuses.