The government has put on hold formal negotiations with Tokyo regarding the possible joint development of the Tak-Mukdahan electric rail route.
Transport Minister Prajin Juntong said the talks have been suspended due to current political changes in Japan.
ACM Prajin said Japan will have to form a new government before talks on the dual-track rail route can resume.
- Previously, on Nov 20: Japan likely to ink rail deal soon
Japanese Prime Minister Shinzo Abe dissolved the lower house of parliament on Nov 21, setting the stage for a snap election on Dec 14.
Informal talks between officials on both sides will continue, despite the temporary suspension of formal negotiations, ACM Prajin said.
Last month, a Thai source said the government is likely to reach an agreement with Tokyo to jointly build one of two proposed dual-track electric train routes.
Tracks in the scheme will be 1.43-metres wide.
The Government House source said he expected the agreement to be signed during Prime Minister Prayut Chan-o-cha's official visit to Japan that would follow his return from a meeting in South Korea in December.
Gen Prayut will attend the two-day Asean-South Korea Commemorative Summit beginning on Thursday, and was scheduled to fly to Japan for an official visit on Friday.
The source said the government was expected to allow Japan to operate the Tak-Mukdahan route connecting western and eastern Thailand.
The National Legislative Assembly has meanwhile endorsed a draft memorandum of understanding (MoU) between Thailand and China to cooperate on another dual-track trains project.
ACM Prajin said on Friday that Prime Minister Prayut Chan-o-cha will sign the MoU with China by the third week of this month.
The MoU sets out bilateral cooperation on projects to construct the 734km Nong Khai-Nakhon Ratchasima-Kaeng Khoi-Map Ta Phut route, and the 133km Kaeng Khoi-Bangkok route.
ACM Prajin, who is leading the negotiation team with China, said further talks to iron out details of the projects are in the pipeline.
A source at the Transport Ministry said the MoU says both the construction and the system-wide development of the rail link project will be China's responsibility.
Thailand will allow China to conduct a feasibility study for the project, said the source, adding construction should begin in 2016 and will be managed by a joint Thai-Chinese committee.
The completion date for both routes is 2021.
ACM Prajin also revealed the cost of three new motorway projects that are due to be constructed next year.
The 190km Bang Pa-in-Saraburi-Nakhon Ratchasima motorway will come in at 84 billion baht, the 96km Bang Yai-Ban Pong-Kanchanaburi motorway will cost 55.6 billion baht, while 14 billion baht will be spent on the 32km Pattaya-Map Ta Phut motorway.
The Pattaya-Map Ta Phut project will probably start first since land expropriation money had been set aside, ACM Prajin said, adding that extra cash to finance the new road will come from the Motorway Fund, which earns revenue through toll fees from motorists.
"Several countries, such as South Korea, China, and Japan, have now expressed their interest in providing loans for the other two motorway projects," he said.