UPDATE 1-Vietnam to propose oil, gas development with Japan-media

* Vietnam to put development of 20 blocks on table-Nikkei

* To seek investments for projects worth $24.8 bln-report

* Vietnam to hold briefing for Japan in July-report (Adds details)

TOKYO, June 13 (Reuters) - Vietnam's state oil and gas group Petrovietnam plans to invite Japanese firms to join it in the joint development of about 20 oil and gas blocks in the South China Sea, the Nikkei business daily said on Wednesday.

Petrovietnam will hold a briefing session for Japanese firms in early July, the unsourced report said. Japanese firms will also be given a chance to invest in infrastructure projects, including oil refineries and coal-fired power plants, totalling $24.8 billion, it said.

State-owned Petrovietnam held a similar briefing in Tokyo in June 2010, inviting Japanese investments in 28 Vietnamese projects in downstream oil, power plants, finance and real estate, totalling $23.8 billion.

An official with the Japan External Trade Organisation (JETRO), which helped organise the 2010 briefing, said no new briefing had been planned as yet.

A number of Japanese firms have been involved in energy projects in Vietnam, including JX Holdings and Idemitsu Kosan Co in the upstream sector.

Japan's JX Nippon Oil and Energy, a unit of JX Holdings, has been also considering teaming up with Petrovietnam for the expansion plan of Vietnam's Dung Quat oil refinery. (Reporting by Osamu Tsukimori; Editing by Richard Pullin)