New Delhi, Dec. 22: Delhi lieutenant-governor Najeeb Jung, whose three-and-a-half-year tenure was marked by confrontations with the Aam Aadmi Party government, resigned today citing personal reasons. Both the Centre and chief minister Arvind Kejriwal said the decision had taken them by surprise.

Kejriwal had often accused Jung of being an "agent" of the Narendra Modi government.

"Lt Governor Najeeb Jung has submitted his resignation to the Government of India. He thanks the Prime Minister for all the help and cooperation he received during his tenure," the LG's office said.

The immediate trigger behind the resignation remained a puzzle till late tonight but sources in the BJP hinted that Jung, caught in the protracted confrontation between the Centre and the Kejriwal regime, wasn't being able to take the pressure any more.

Kejriwal and Jung had clashed over administrative jurisdiction, before the fight reached the judiciary. Earlier this year, Delhi High Court had ruled that the LG was the state's administrative head. The matter is now pending in the Supreme Court.

"His resignation is for personal reasons," said Ajay Chaudhary, officer on special duty in the lieutenant-governor's office. "LG wanted to spend time with his family and return to his first love, academics." Jung, 65, was vice-chancellor of Jamia Millia Islamia before he took over as lieutenant-governor in July 2013.

Union home secretary Rajiv Mehrishi told reporters Jung had met him on Tuesday about some issues regarding Delhi. "But he did not give any indication of his impending resignation."

Kejriwal tweeted: "Sh Jung's resignation is a surprise to me. My best wishes in all his future endeavours."

An undated letter by Jung that surfaced today did little to clear the mystery. In the letter to Mehrishi, Jung says he would be on a "private visit" to Goa from December 25 to January 1, suggesting he had not decided to quit then. "(The) Chief Secretary will keep in touch with me about important developments," he says, according to PTI.

Former Delhi police commissioner Ajay Raj Sharma is said to be in the reckoning to succeed Jung.