Japanese Prime Minister Shinzo Abe discussed strengthening cooperation with gas-rich Qatar as he met emir Sheikh Tamim al-Thani in Doha on Wednesday as part of a regional tour.
The two leaders agreed to strengthen cooperation in the political and security fields, they said in a joint statement.
Abe's tour of the Gulf is seen as his latest push to promote nuclear technology exports.
And the Japanese government says Qatar and Kuwait have shown an interest in nuclear safety, out of concerns that neighbouring countries plan to build nuclear plants.
In May, Japan signed a nuclear cooperation deal with another Gulf state, the United Arab Emirates, during a similar visit by Abe.
A day later, he visited Turkey and signed a long-awaited deal to build a sprawling nuclear power plant on the country's Black Sea coast, in a milestone for the Japanese nuclear industry.
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Japan has touted its atomic expertise as an important export despite the 2011 catastrophe at the tsunami-hit Fukushima Daiichi nuclear power plant, where multiple meltdowns cast a pall of radiation over a swathe of the country's northeast.
Qatar and Japan also agreed to expand "bilateral cooperation on infrastructure development in Qatar," said Wednesday's statement.
The Gulf state is building its infrastructure from scratch after winning the right to host the 2022 football World Cup.
On Tuesday, it signed a memorandum of understanding with South Korea for cooperation in the construction sector.
Abe began his tour of Djibouti and the rich Arab states of the Gulf this week, taking him to Bahrain then Kuwait before he arrived in Doha on Wednesday where he took part in a business forum.
Qatar and Japan "reiterate the importance of the stability of the global energy market and welcome Qatar's commitment to supplying oil and LNG (liquified natural gas) to Japan in a manner that is beneficial to both countries and that contributes to bringing stability to the markets," they said.
Qatar is the largest gas exporter to Japan, with deliveries amounting to 15.5 million tonnes in 2012, according to the Trade Statistics of Japan.
It is also the third largest exporter of crude oil, supplying about 394,000 barrels of oil per day to Japan in 2012.