Updates with source confirmation on Akazawa's U.S. visit in paragraphs 1 and 4

By Tamiyuki Kihara and Kantaro Komiya

TOKYO, Aug 26 (Reuters) - The United States will make an announcement this week on Japan's $550 billion investment in the U.S., Commerce Secretary Howard Lutnick said, with a top Japanese trade envoy planning to visit Washington to formalise the package.

"The Japanese agreement, which we're going to announce later this week, that's $550 billion at the hand of Donald Trump," Lutnick told the Ingraham Angle show on Fox News on Monday night.

The Japanese funds could be used for the manufacturing of products such as semiconductors, antibiotics or rare earths in the U.S., Lutnick added.

Tokyo's top trade negotiator Ryosei Akazawa plans to visit the U.S. this week to craft a written confirmation on the financial details of the package, such as the split of investment returns between the U.S. and Japan, a government source close to the negotiations told Reuters.

Washington and Tokyo agreed in July to set a reduced 15% tariff on imports from Japan in exchange for a $550 billion package of U.S.-bound investment through government-backed loans and guarantees, but details of its contents remain obscure.

While Trump has touted the package as "our money to invest" and said the U.S. would retain 90% of the profits earned, Japanese officials have stressed that the investments will be determined based on whether they will also benefit Japan.

SoftBank Group's 9984.T $2 billion investment in Intel INTC.O announced last week was not part of the package at the moment, a Japanese government source has said.

Akazawa, speaking at a regular Tuesday briefing, said his next U.S. trip was not decided and declined to comment on Lutnick's remarks. Tokyo will keep pressing Washington to implement the deal to cut U.S. tariffs on Japanese goods soon, he added.

The U.S. has urged Japan to have a written agreement on the investment plans, but Japan would prefer to keep the deal less legally-binding, the Nikkei business daily reported earlier on Tuesday.

The lack of a clear document on the trade agreement had created confusion in Tokyo about tariff rates until Lutnick and U.S. Treasury Secretary Scott Bessent clarified earlier this month that Japanese goods were exempt from overlapping levies and an earlier presidential order would be amended.

Lutnick and Bessent also promised, during Akazawa's previous visit on August 7, that Trump would issue another order to lower tariffs on Japanese cars to 15% from 27.5%, but did not specify when.

Japanese Prime Minister Shigeru Ishiba has said Tokyo did not seek a written trade agreement with Washington because it wanted a swift resolution and to ensure Trump's tariffs on key Japanese exports such as autos were lowered quickly.

Ishiba's support rate has surged in recent polls thanks in part to the trade deal, even after his ruling coalition lost its majority in an upper house election last month.

(Reporting by Tamiyuki Kihara and Kantaro Komiya; Editing by Kate Mayberry and Sonali Paul)

((kantaro.komiya@thomsonreuters.com; X: @kantarokomiya;))