Hitachi Limited and Mitsubishi Heavy Industries, two of Japan’s biggest manufacturers, are considering merging several of their infrastructure operations.

With combined annual sales of more than $150 billion, the potential merger would create one of the world’s biggest infrastructure firms. Shares of both Hitachi and Mitsubishi rose Thursday, hours after Hitachi President Hiroaki Nakanishi announced the firms had agreed to hold talks.

But both companies later issued statements denying they were in negotiations.

Hitachi is Japan’s biggest electronics firm, while Mitsubishi is the nation’s leading heavy machinery maker. Both companies are also involved in building nuclear reactors, a sector which is facing an uncertain future in the aftermath of the Fukushima nuclear plant disaster.

Japan’s biggest conglomerates are under pressure to consolidate and merge operations, thanks to a shrinking domestic market and excess capacity.

Hitachi announced on Wednesday that it is considering turning over all of its television building operations to overseas manufacturers.