* Benin president says terrorism international problem
* Harper concerned but not planning direct military mission
OTTAWA, Jan 8 (Reuters) - The head of the African Union, Benin President Boni Yayi, called on Tuesday for a global coalition to intervene against Islamist rebels in northern Mali, but Canadian Prime Minister Stephen Harper said he had no plans to join the U.N.-sanctioned force.
The capture of the northern two-thirds of Mali by Islamist groups has sown fears that it could become a center for radicals to plot international attacks, and Yayi said terrorism was an international problem that required an international response.
"It's not...a purely African question. It's a world question, an international question," Yayi told a news conference with Harper after their ministers signed a foreign investment protection agreement.
Harper said Canada would provide humanitarian aid and signaled great concern about the situation, but said: "The government of Canada is not considering a direct Canadian military mission."
The 15-nation U.N. Security Council in December unanimously authorized the deployment of an African-led military force to help defeat al Qaeda and other Islamist militants in northern Mali. (Reporting by David Ljunggren and Louise Egan; Editing by Cynthia Osterman; Writing by Randall Palmer)