By Dustin Volz

WASHINGTON (Reuters) - A senior U.S. Justice Department official who oversaw efforts to prosecute Islamic State sympathizers and pursue cyber criminals is leaving the Obama administration next month, he told Reuters on Tuesday.

Assistant Attorney General John Carlin, chief of the national security division at the Justice Department, is departing on Oct. 15, less than a month before the U.S. presidential election.

The departure comes as the Obama administration has struggled to develop clear guidelines on how to pursue hacking amid growing threats posed by foreign nation-states and criminal groups.

In an interview, Carlin, 43, declined to say where he was headed next. He intends to spend time with his family before starting a new job, likely involved in cyber security, he said.

Carlin, who has served in government for more than 15 years, oversaw a range of prominent cases in three and a half years since assuming an acting rank of the Justice Department's top national security lawyer in March 2013, including the prosecution of one of the 2013 Boston Marathon bombers.

He was confirmed full-time to the position in a 99-1 vote by the U.S. Senate in April 2014.

Carlin focused on pursuing cyber criminals during his tenure running the national security division.

His tenure included the unprecedented indictment of five Chinese military hackers in 2014 for alleged hacking into six U.S. companies in order to steal trade secrets, and the indictment of Iranian hackers earlier this year for alleged hacks on U.S. financial institutions and a New York dam.

In a statement, Attorney General Loretta Lynch said Carlin was a "trusted and tireless leader" who "used all the tools at his disposal to enhance our public safety and uphold our national security."

Carlin will be replaced by Mary McCord, principal deputy assistant attorney general, on an acting basis, the Justice Department said.

Through a combination of legal cases, diplomatic sanctions and an effort to publicly name and shame hacking adversaries, Carlin sought to tame what he often called the wild west of cyberspace, where international norms for appropriate cyber activity are nascent or nonexistent.

"We've laid a strong foundation in cyber, but we've got to do more, faster, given the state of the threat," Carlin told Reuters. He said he hoped the next presidential administration could further "institutionalize" consequences from cyber crime.

Most recently Carlin announced this month the formation of a threat analysis team to study potential national security challenges posed by self-driving cars, medical devices and other Internet-connected tools.

Carlin’s appointment in early 2014 coincided with territorial gains by Islamic State in Iraq and Syria that propelled the militant group to global notoriety. Since then, the department has prosecuted dozens of people on counts related to Islamic State: more than 100 people have been charged since 2014 in public federal cases.

Under Carlin, the national security division has also ramped up the Justice Department’s efforts to combat what it sees as a rising threat from domestic anti-government extremists.

(Reporting by Dustin Volz; additional reporting by Julia Harte and Julia Edwards; Editing by Bernard Orr)