Four nuclear power plant operators in western Japan are joining forces to strengthen safety measures and reduce costs, the first broad tie-up by major utilities in the area, sources close to the matter said Tuesday.

Amid increasing costs for safety upgrades in the wake of stricter regulations following the 2011 Fukushima nuclear disaster, pressure is also building on utilities ahead of electricity market deregulation in Japan.

The sources said Kansai Electric Power Co., Chugoku Electric Power Co., Shikoku Electric Power Co. and Kyushu Electric Power Co. will team up for emergency responses, technology exchanges and sharing know-how on safety improvements needed to restart idled reactors.

The four regional power companies aim to finalize the partnership arrangement by the end of this month, the sources said.

The utilities will seek to establish operations for closer contact in the event of severe accidents such as a meltdown, while also eyeing shared portable generators and pumping vehicles.

The companies will also exchange decommissioning technology, which requires special expertise and can take more than three decades to complete.

In the face of stricter safety regulations, the four utilities plan to scrap their aging reactors.

Kansai Electric decided to retire two reactors at its Mihama nuclear plant and the three other operators also plan to shut one reactor each, at Chugoku Electric's Shimane, Shikoku Electric's Ikata and Kyushu Electric's Genkai nuclear plants.

Kyushu Electric rebooted two reactors at its Sendai nuclear complex last year and Kansai Electric reactivated two reactors at its Takahama plant earlier this year, though a court injunction in March brought them back to a halt.

A reactor at Shikoku Electric's Ikata plant is expected to be restarted in late July.