Japan has agreed with the United States to accelerate talks on the first batch of deals under Japan's $550 billion investment package as some issues still need to be worked out, Trade Minister Ryosei Akazawa said Thursday.

"As there remain areas where Japan and the United States need further coordination, we agreed to work closely together to develop projects," Akazawa told reporters in Washington, D.C.

Japan has been under pressure to move faster on implementing the investment package agreed as part of Tokyo's deal with Washington to lower tariffs on Japanese exports.

Asked about the issues that need to be resolved, Akazawa said it takes time to assess various metrics, such as projected interest rates for each project.

"Because of that, the talks have become extremely tough. I cannot say at this point when or what kind of projects will be finalized," Akazawa said, adding that the talks are being conducted with Prime Minister Sanae Takaichi's planned U.S. visit in mind to ensure it is fruitful.

President Donald Trump is threatening to raise tariffs on South Korea, which he accuses of dragging its feet on adopting a similar agreement reached last year.

Japan's investment package would include equity, loans and loan guarantees from state-owned agencies Japan Bank for International Cooperation and Nippon Export and Investment Insurance.