He is also dealing with the fallout from a suspected US air strike on a hospital in the Afghan city of Kunduz that killed 22 people, some of whom burned to death in their beds.
The five-day trip to Spain, Italy, Britain and a NATO ministerial summit in Brussels is intended to recognize the work of ally nations as they scramble to tackle the refugee crisis as well as respond to Russian aggression in eastern Ukraine.
The tour comes at a fraught time for Carter, who started in the Pentagon's top job in February and who faces pressure at home over Syria and a simmering scandal involving military officials allegedly cherry-picking intelligence.
While in Spain, Carter will visit a base in Moron de la Frontera, where a permanent force of 2,200 US marines has been established. The facility was bolstered in the wake of the 2012 attack on a US mission in Benghazi, eastern Libya.
The main mission of the Special-Purpose Marine Air-Ground Task Force Crisis Response (MAGTF) unit is to protect US embassies in Africa, evacuate civilians in difficulty, or intervene in conflicts or humanitarian crises.
Carter has appeared reluctant to stray from official White House talking points and critics say he is overly cautious in his public pronouncements.
The Pentagon is under massive pressure over its efforts to intervene in Syria. While the White House does not want to commit ground forces to another difficult Middle East conflict, opponents are outraged by what they see as a lack of US action to halt the war that has claimed some 250,000 lives and displaced millions.

Latest News from World News Desk