The firm's finances have long suffered as its numerous stakes in foreign mobile operators have slumped in value.

But now both DoCoMo and US operator Cingular, reports say, are looking to take control at US firm AT&T Wireless - in which DoCoMo has a 17% stake.

DoCoMo's shares rose 5,000 yen to 237,000 yen, bucking a falling market.

Earlier on Wednesday, the company's shares had risen as much as 5%.

AT&T Wireless, which was spun off from US phone giant AT&T, is currently worth about $27bn on its stock market valuation.

Reports in newspapers and wire services suggest that Cingular - owned by SBC and BellSouth - is offering slightly more than that.

Cingular is the US' number two mobile carrier with 23.4 million customers, trailing Verizon Wireless's 36 million by some distance but ahead of the 21.9 million claimed by AT&T Wireless.

DoCoMo could offer more money, but could be handicapped by investor caution about its foreign investment strategy.

The minority stakes it took in a range of operators, including KPN in the Netherlands and 3 in the UK, cost it a 1.12 trillion yen write-down in 2001 and 2002, pushing it deep into the red.