President Obama on Tuesday formally abandoned his pledge to bring U.S. troop levels in Afghanistan down to 5,000 by the end of this year, saying the current force of about 10,000 will remain there into 2016.

Yet Obama also firmly reiterated his goal of completely ending the military mission in Afghanistan before he leaves office in January 2017.

Obama acknowledged that the change will mean longer deployments for some troops and more strain on the military but said the additional effort may be critical to securing long-term success in Afghanistan.

"It means some folks are going to be rotating back into Afghanistan for a few extra months relative to what otherwise would have been the case." Obama said at a White House news conference alongside Afghan President Ashraf Ghani.

"We are essentially moving the drawdown pace over to the right for several months … in part because we want to make sure we are doing everything we can to help the Afghan security forces succeed, so we don't have to go back, so we don't have to respond in an emergency because terrorist activities are being launched out of Afghanistan," Obama said.

"We are on a path to do that, and it was my assessment as commander in chief, it made sense for us to provide a few extra months for us to be able to help in things like logistics…training, advising and strategic input," the president said.

In effect, Obama said he will back away from the commitment that he made in May 2014 to drawdown today's force of 10,000 to about 5,000 by the end of this year. The rise of Islamic State militants in Iraq last summer has fueled concerns that Obama's initial plan was pulling U.S. forces out too quickly.

Now, Obama says he will give the Afghanistan mission's commanding general, Army Gen. John Campbell, the "flexibility" to keep the current force level through the end of the year and complete the drawdown by the end of 2016.

In response to a question from a Military Times reporter, Obama emphasized that his commitment to end the military mission before leaving office remains intact.

"The date for us to have completed our drawdown will not change," Obama said. "But it is my judgment, and that of Gen. Campbell, that providing this additional time frame during this fighting seasons for us to be able to help the afghan fighting forces succeed is well worth it."

Obama said goals underlying the mission will remain unchanged and the slightly larger force next year will continue to perform a non-combat advise-and-assist mission as well as to conduct limited counter-terrorism operations against the remnants of al Qaeda and in some cases the Taliban.

The U.S. Army will be most affected by the change in schedule. Yet it is unclear whether the Army will have to issue a large number of new deployment orders or whether the extended mission will be fulfilled by the troops who are scheduled to go to Afghanistan later this year with nine- and 12-month deployment orders.

"This will mean that there are going to be some of our [military] folks who are Afghanistan under the schedule who would have been home. But it's important to keep in perspective that we have gone down from over 100,000 to under 10,000, that they are not on the front lines because they are not in combat role. And we are doing all that we can do to make sure that force protection is a priority," Obama said.

The new policy for "flexibility" also will likely mean that the U.S. will keep the airfields in Kandahar in the south and Jalalabad in the east open into 2016. Obama's previous plan was to limit the U.S. military mission next year to the area around Kabul.

Obama noted that the U.S force in Afghanistan has not reported any troops killed in action for more than 90 days since the U.S. "combat mission" officially ended.

A White House spokesman recently clarified that Obama's goal of ending the military mission by the end of 2016 means a military force of about 1,000 would remain to support a "Kabul-based embassy presence."

Concerns about the Afghan security forces have intensified over the past year due to high casualty rates. More than 4,600 Afghan soldiers and police were killed in 2014, a slight uptick from the previous year. That rate is "unsustainable," according to Army Lt. Gen. Joseph Anderson, a senior commander for U.S. and NATO forces in Afghanistan.

Afghan President Ghani made the trip to Washington in part to lobby top U.S. government officials for continued financial and military support. On Monday, he visited the Pentagon and thanked a group of U.S. troops who have deployed to Afghanistan for their service. On Tuesday, he visited Arlington National Cemetery.

At the White House on Tuesday, Ghani said keeping more U.S. troops in Afghanistan next year will help secure the gains that the American military has made over the past 14 years.

"The 2,215 Americans that have died must not die in vain. They must leave behind a legacy of a stable Afghanistan," Ghani said at the White House news conference.