Japan's Toshiba said Wednesday it will raise its stake in US atomic power-plant giant Westinghouse Electric, as it eyes overseas deals after the Fukushima disaster depressed domestic demand.

The firm said it would pay 125 billion yen ($1.6 billion) for the 20 percent stake in Westinghouse owned by US-based Shaw Group, lifting its holding to 87 percent.

It said the purchase would be financed through "immediately available cash and/or loans".

Investors were unimpressed, sending Toshiba's Tokyo-listed shares tumbling 4.18 percent to 252 yen by the close.

In an earlier agreement with Toshiba, Shaw, a Louisiana-based engineering firm, had the option to sell all or part of its 20 percent stake to the Japanese giant, which said it was eyeing new investment partners.

"Toshiba has received interest from potential partners regarding the acquisition of a stake in Westinghouse, and is open to talks on the condition that Toshiba retains a majority stake," the Japanese firm said.

Westinghouse is currently building four nuclear reactors in the United States and four in China, the Toshiba statement said.

It is believed to be seeking an alliance with multiple partners to help tap China and other emerging nations after anti-nuclear sentiment in Japan dashed interest in building any new reactors in the disaster-stricken nation.

Last year's March 11 quake-tsunami disaster sparked reactor meltdowns at the Fukushima Daiichi plant, spewing radiation over a large area in the worst atomic crisis for a generation.