Donna Hanover held a separate news conference

Mr Giuliani made the announcement of the separation plans to reporters at an emotional news conference in Manhattan, saying he and his wife, journalist and actress Donna Hanover, were already leading separate lives.

"It's been a very painful road. I'm very sad and I feel terrible.

"Over the course of some period of time, in many ways we've grown to live independent and separate lives, and we should probably strive towards formalising that."

Mr Giuliani said he expected his decision to elicit some sympathy and some anger.

"I have to try to do what I think is right for me, my family, for the people that are involved, and I think this is the right statement to make and the right direction to go."

Today's turn of events brings me great sadness - I had hoped that we could keep this marriage together

Donna Hanover

He added: "I'd like to get it resolved pretty soon."

The couple have been married for 16 years, but they have rarely appeared together in recent years. They have two children, a boy and girl aged 14 and 10.

A distressed Ms Hanover made a separate announcement outside the mayor's residence, Gracie Mansion.

"Today's turn of events brings me great sadness. I had hoped that we could keep this marriage together," she said.

Only last Saturday, Ms Hanover had told reporters that "this marriage and this man have been very precious to me," and pledged to support him in his fight against cancer.

The couple in happier times, pictured in 1993

Mr Giuliani's friendship with nurse Judith Nathan has generated much media interest in New York since they were photographed last week leaving a restaurant together.

He gave more details of their relationship at Wednesday's news conference.

"Judith Nathan is a very, very fine person," he said.

"She's been a very good friend to me, before I had to deal with the decisions that I have to make about my illness and what to do about it, and I rely on her, and she helps me a great deal and I'm going to need her more now than maybe I did before."

His wife, he added, was "a wonderful woman" and "a wonderful mother".