Wellington  -  New Zealand police launched an investigation into the background of the head of the country's Immigration Service on Wednesday after she resigned amid suggestions that she had faked her academic qualifications.

Mary Anne Thompson, 53, who was a high-flying civil servant, quit suddenly on Tuesday after "serious questions" were raised about her claim to have a doctorate from the influential London School of Economics.

Thompson was already under investigation for her role in her department's approval of residency permits for three members of her husband's extended family from the Pacific island state of Kiribati.

An official report, released after media inquiries, revealed that Thompson had helped the family fill in application forms and senior staff members were pressured into approving them although the current immigration quota for Kiribati was already oversubscribed.

Thompson was regarded as one of the country's most trusted civil servants, having risen to be the highest-ranking female official in the Treasury and a senior executive in the Department of Prime Minister and Cabinet before moving to head the Immigration Service in the Department of Labour in 2004.

A statement on Tuesday said she had resigned "in the interests of the department and the wider public service."

The deputy State Services Commissioner, Iain Rennie, said, "Information has been provided to me that raises serious questions about the qualifications Mary Anne Thompson said she held in applying for senior roles in the New Zealand Public Service."

He said he referred the matter to police on the advice of the government law office. (dpa)