"The president has formally asked the AU for a 20,000-strong peacekeeping force to help in collecting millions of small arms known to be owned by the Somali people," AU spokesman Adam Thiam said on Saturday.
He said the request would be considered by the AU's Peace and Security Council which is due to meet on Monday.
Yusuf made the request to AU chairman Alpha Umar Konare during a meeting with top AU officials on Saturday in the Ethiopian capital Addis Ababa.
Yusuf was elected as Somalia's president after almost two years of stop-start talks held in neighbouring Kenya because of insecurity at home. He made an appeal for international peacekeepers at his swearing in ceremony last week.
"We would like to participate in the stabilisation of the
EU foreign policy chief
EU foreign policy chief Javier Solana, also on a visit to AU headquarters in Addis Ababa, said the European Union would consider helping to train Somali security forces.
"We would like to participate in the stabilisation of the country," Solana said.
Diplomats say Yusuf risks leading a government in exile if he is unable to return quickly to Mogadishu and that the legitimacy of his government hinges on gaining control of the anarchic country.
Somalia descended into chaos in 1991 when president Muhammad Siad Barri was overthrown, and has since been controlled by rival factions.