WELLINGTON, Jan. 13-- The head of New Zealand's electronic and foreign intelligence agency is stepping down, the government said Tuesday, ending a three-year tenure overshadowed by accusations of illegal spying and politicization of the intelligence services.

Government Communications Security Bureau director Ian Fletcher was stepping down for family reasons, Minister Responsible for the GCSB Christopher Finlayson said in a statement.

Fletcher had been instrumental in the "significant improvements " that had taken place at the GCSB, where he had led the implementation a review of the GCSB's activities after it was found to have illegally spied on more than 80 New Zealand residents and citizens before 2012.

The review had resulted in increased public openness and accountability of the GCSB, Finlayson said.

"The statutory review of the intelligence agencies, due to start shortly, will likely herald a further period of change," said Finlayson, adding that Fletcher's early departure on Feb. 27 would allow a new boss to oversee future changes.

The brother of an old school friend of Prime Minister John Key, Fletcher had held senior public service roles in the United Kingdom, Australia and New Zealand before he was controversially picked by Key to head the GCSB.

Fletcher was in charge when the government passed a controversial law in August 2013 to extend the spying powers of the GCSB, so it could spy on New Zealand citizens and residents.

In the run-up to the general election in September last year, U. S. National Security Agency (NSA) whistleblower Edward Snowden claimed the NSA had unfettered access to all New Zealand electronic communications, aided by New Zealand's GCSB.

Leader of the main opposition Labour Party Andrew Little said the resignation was a "big surprise" as he and Fletcher had discussed developing relationships between their offices late last year.

"What I find intriguing is, in the published statement, the references to the upcoming review of the security agencies and whether or not he's now been told of something that he finds disagreeable, and this is the real reason he's going," Little told Radio New Zealand.

The opposition Green Party is calling for Parliamentary cross- bench involvement in the selection of a new director to ensure political neutrality of the security services.

"John Key compromised the neutrality of the GCSB both in Mr Fletcher's appointment process and in the way used the bureau's information over the past three years. He has treated the GCSB as his own personal protection service," Green Party security and intelligence spokesman Kennedy Graham said in a statement.