(CNN) -- Europe's largest powers appeared Wednesday to be united in their goal of removing al Qaeda-linked militants from the West African nation of Mali, where Islamist rebels are fighting to overthrow Mali's government.
A quarter-million people have fled Mali -- twice the number who have fled fighting in Syria -- and stirred international fears that Mali will become Africa's next haven for terrorists.
French troops and warplanes have been helping Malian government forces stop Islamists from overrunning the capital, Bamako, an effort they're calling Operation Serval. French President Francois Hollande told reporters in Paris on Wednesday that it was a "necessary decision" to go into the country, a former French colony.
"If we had not acted when we did, it probably would have fallen into the hands of terrorists," he said. France is "doing it to help the Malian people."
French Defense Minister Jean-Yves Le Drian said Tuesday that French troops and warplanes joined the battle last week on the side of Malian government forces, and prevented the Islamists from capturing the city of Mopti.
Germany's Defense Ministry announced Wednesday it will contribute two Transall transport planes to the offensive.
Italy said it is "ready for a logistical support operation" in Mali, Foreign Minister Giulio Terzi told a senate hearing on international missions Wednesday.
Belgium's defense minister said Tuesday that Brussels will send two C-130 transport planes, two medical helicopters and 75 soldiers to Mali.
Canada, which is supplying logistical support to the mission, sent a military transport plane to France, where it was loaded Tuesday with supplies and personnel to continue on to Mali.
The United States has promised to help the effort, Defense Secretary Leon Panetta said Monday. State Department spokeswoman Victoria Nuland said the United States is reviewing requests from the French, but that no decisions have been made on specifics.
A spokesman for the Turkish Foreign Ministry, Selcuk Unal, said Turkey was watching the developments in Mali with concern and added that his government did not prefer unilateral actions and operations, according to the semi-official Turkish news Anadolu Agency. Unal noted that Turkey has issued a travel warning for Mali.
The operation, though, is being led by France, those countries say.
Hollande has said France had three aims: stopping the "terrorist aggression" from the north; securing Bamako and safeguarding French nationals there; and enabling Mali to recover its territorial integrity.
He stressed that France was in Mali at the request of its government, with the support of its neighbors and world powers, and within the framework of international law.
"If we had not taken up our responsibility and if on Friday morning we had not acted with this intervention, where would Mali be today?" Hollande asked.
The fighting has spurred the U.N High Commissioner for Refugees to prepare for a possible flow of refugees from Mali into neighboring countries of Niger, Mauritania and Burkina Faso.
"We have been preparing contingency plans and getting ready on the ground to ensure that we can deal with various possible scenarios," said Karl Steinacker, the UNHCR representative in Niger. "The provision of water, sanitation and hygiene, health, education, protection from sexual and gender-based violence, and child protection are our main priorities," he added.
Mali was one of the most successful democracies in Africa until insurgents began trying to take it over.
Besides taking many lives, the insurgents have destroyed historic shrines in Timbuktu that date to the 15th century. The attackers say the shrines offend Sharia law.
Such allegations have spurred the International Criminal Court to launch a war-crimes investigation, its chief prosecutor announced Wednesday. Fatou Bensouda said Mali's government asked the U.N. tribunal to investigate in July, after Islamists had taken control of much of the country.
"The international crimes committed in Mali have deeply shocked the conscience of humanity," Bensouda said Wednesday. "The legal requirements have been met. We will investigate."
The ICC has found "reasonable basis" to support allegations of murder, torture, mutilation, rape and pillaging, Bensouda said.
The human rights group Amnesty International welcomed the announcement, calling it "a crucial step towards justice for the victims." But the group said the ICC should look at human rights abuses committed by all sides in the conflict, including by government troops and the ethnic Tuareg rebels, whose 2012 revolt set the stage for the current conflict.
CNN's Jim Bittermann, Hada Messia and Frederik Pleitgen contributed to this report.