WASHINGTON -- President Barack Obama tapped a highly respected combat commander for the top U.S. military post, signalling that the battles against al Qaeda and Islamic State militants threatening the Middle East and the West remain top priorities for the nation's military despite years of trying to change the focus to Asia.

Announcing his selection of Marine Gen. Joseph Dunford Jr. to be chairman of the Joint Chief of Staff during a Rose Garden ceremony, Obama said America's armed forces must be ready to meet a broad range of challenges, and that Dunford has proven to be one of the military's most highly regarded strategic thinkers.

"We have to keep training Afghan forces and remain relentless against al Qaeda. We have to push back against ISIL and strengthen forces in Syria and build moderate opposition in Syria," said Obama, using an alternate name for the Islamic State group. "We have to stand united with our allies in Europe and keep rebalancing our posture as a Pacific power. We have to keep investing in new capabilities to meet growing threats, including cyberattacks."

As the U.S. started to look beyond the wars in Iraq and Afghanistan, the Pentagon had begun to increase its focus on the Asia Pacific region, where the North Korea threat was escalating and China was flexing its military muscles. But that has been eclipsed by the march of Islamic State militants across Syria and Iraq, and the group's effort to expand to other regions and import the fight to the West.

In choosing Dunford, Obama picked a battle commander who led forces in the initial invasion into Iraq and more recently was in charge of the Afghanistan war coalition during a key transitional period during 2013-14. And if confirmed, Dunford also represents a sense of continuity, succeeding Army Gen. Martin Dempsey, who will have served as chairman for four years. Both men are known as intellectual and charismatic leaders who connect well with their troops.

He is well-connected internationally, often meeting with NATO and other coalition leaders, particularly during his Afghanistan command.

But in the end, such choices often come down to personal relationships.

"I know Joe, I trust him," Obama said. "He has already proven his ability to give me his unvarnished military advice based on his experience on the ground." He added that under Dunford's "steady hand we've achieved key milestones, including the transition to Afghan responsibility for security, historic Afghan elections and the drawdown of U.S. forces."

Obama also chose Gen. Paul J. Selva, a top Air Force officer and pilot, to serve as vice chairman. Selva, who has clocked more than 3,100 hours piloting transport and refuelling aircraft, is currently the head of U.S. Transportation Command. The two officers are expected to be easily confirmed by the Senate.

Dunford's service as the commandant of the U.S. Marine Corps was brief -- he began that job last October. But the rapid promotion is one of several that have marked his fast-tracked military career, which saw him leap from a one-star general to four stars in about three years. He would be only the second Marine to serve as chairman.

He began his career as an infantry officer, and he earned the nickname "Fighting Joe" when he led the Marines' 5th Regimental Combat Team during the 2003 Iraq invasion.

Dunford's most visible military role came in 2013 when he became the top U.S. military commander in Afghanistan. During his 18 months there, he oversaw the ongoing drawdown of U.S. troops, the transition to Afghan military lead in combat operations, and the tumultuous Afghan elections that dragged on and delayed efforts to reach an agreement on the U.S. military's future presence in the country.