UPDATE 1-Bain aims to buy Japan ad agency Asatsu-DK in $1.2 bln deal - source

* Bain to launch tender offer soon for Asatsu-DK, says source

* Nikkei said earlier Bain to pay about 150 bln Y for Asatsu-DK (Recasts to attribute to source, add detail of plan)

TOKYO, Oct 2 (Reuters) - U.S. private equity firm Bain Capital plans to buy Japanese advertising agency Asatsu-DK Inc in a deal that could be worth $1.2 billion or more, a person familiar with the transaction said on Monday.

Bain will launch a tender offer soon for as many shares of Asatsu-DK as possible, the person said, asking not to be identified because he is not in a position to speak to media.

The Nikkei business daily, which reported the buyout earlier on Monday, said Bain would pay about 150 billion yen ($1.33 billion) for the Japanese company.

Asatsu-DK spokeswoman Kaori Nakajima said the report was not something the company had announced.

Asatsu-DK closed at 3,180 yen on Monday, which gives the firm a value of 132 billion yen.

A consortium led by Bain Capital signed an $18 billion deal last week to buy Toshiba Corp's chip unit. ($1 = 112.8700 yen) (Reporting by Junko Fijita; Additional reporting by Chris Gallagher and Chang-Ran Kim; Editing by William Mallard and Muralikumar Anantharaman)