Hagel's last Afghan trip as defense chief

• Hagel's unannounced visit will include other stops in the region


• The trip follows a recent announcement that he will step down as defense chief


• He has served as defense secretary since last year

(CNN) -- Outgoing U.S. Defense Secretary Chuck Hagel arrived in Afghanistan on Saturday for his last trip there as Pentagon chief.

The trip will focus on assessing the nation as the United States begins the drawdown of its forces in the New Year, he said.

Kabul has seen an uptick in Taliban attacks in recent weeks, a sign of instability that he said comes as no surprise.

"It's predictable that they would do everything they could and continue to do to try to disrupt and discourage the new government of President Ghani," he said.

Despite the attacks, the Pentagon said Afghan forces are performing "well," and are now in the lead on 99% of the missions.

"The gaps are in aviation and ISR (intelligence, surveillance, and reconnaissance)," a senior defense official told reporters on the flight to Afghanistan.

Hagel plans to bring up concerns about security in Kabul when he meets with the new Afghan President Mohammad Ashraf Ghani and Chief Executive Abdullah Abdullah.

This is his fourth and last visit to Afghanistan as defense secretary.

His first trip to Afghanistan was 12 years ago as part of a Congressional delegation.

Asked by CNN how he would define victory more than a decade later Hagel said the people of Afghanistan are far better off today than they were 13 years ago, citing an elected government and a national security force.

"They're not completely there yet, but they've come a long way," Hagel said. "That's to the credit certainly of the United States, the sacrifice, the blood and the treasure that we've made there."

His visit comes after the establishment of a new unity government in the fall, which Hagel will express strong support for during his trip, a second senior defense official said.

The drawdown of U.S. forces in Afghanistan will be "gradual" compared with the withdrawal of troops from Iraq, the first official said.

The U.S. will have 9,800 troops in Afghanistan at the start of 2015. By the following year in 2016, the number of troops will slide down to 5,500 and by 2017 the coalition will consolidate to Kabul.

Maintaining a troop presence will allow the U.S. to monitor the progress of the Afghan security forces over time, according to the first official.

"The Afghan people and the Afghan government ...have asked us to stay," Hagel said contrasting the drawdown to the withdrawal troops in Iraq, where the U.S. could not negotiate an agreement that would allow a residual force in the country.

The trip to Kabul follows Kabul's announcement last month that he will step down as soon as the Senate confirms his successor. President Barack Obama has said he will nominate Ashton Carter to replace him.

Hagel, who has served as defense secretary since February last year, was forced out by Obama, several sources told CNN.

During remarks announcing his resignation, Obama praised him as an "exemplary" defense secretary, calling him critical to various national security accomplishments during his tenure.

He said Hagel's resignation was his own choice.

A critic of the Iraq war, Hagel took over from his predecessor Robert Gates to oversee the draw down from Afghanistan and a heavily cut Pentagon budget.

The former Nebraska senator was the last Republican in Obama's Cabinet. He is a Vietnam combat veteran.

Hagel's unannounced visit will include stops in other countries in the region.

CNN's Barbara Starr and Faith Karimi contributed to this report.