Toshiba has boosted its stake in US nuclear power plant builder Westinghouse Electric to 87 percent, the company said Monday, as it eyes atomic opportunities outside disaster-struck Japan.

The Japanese technology conglomerate said it paid about 125 billion yen ($1.42 billion) for a 20 percent holding in Westinghouse held by US-based engineering firm The Shaw Group.

The deal announced Monday finalised an option that Shaw exercised in October to sell its entire stake in Westinghouse to Toshiba.

Last month, Toshiba said it was in talks with three parties about selling a stake of up to 16 percent in Westinghouse, while keeping its majority stake.

On Monday, Toshiba said it "is considering welcoming new investment partners on the premise that we hold a majority share in Westinghouse".

The firm's statement added that partners would be chosen based on "whether we would be able to share visions and long-term business strategy, whether synergy effect with Westinghouse is expected, and an appropriate estimate of Westinghouse's corporate value is provided, among others".

Japanese firms have been looking overseas as demand for new nuclear plants remains uncertain in the wake of the 2011 Fukushima crisis, the worst atomic accident in a generation that was caused by a quake-sparked tsunami.