A Toshiba logo is seen in Tokyo, May 9, 2011. Tomohiro Ohsumi/Bloomberg via Getty Images

Japan's Toshiba Corp. is considering a large writedown for its Westinghouse nuclear power unit, a newspaper report said on Friday, while the company confirmed that U.S. authorities are probing accounting at its U.S. units.

The developments cast a shadow over Toshiba's efforts to draw a line under last year's $1.3 billion accounting scandal by streamlining its bloated businesses, whose poor performances had been masked by years of false bookkeeping.

The Asahi newspaper reported that Toshiba is considering a 200 billion yen ($1.8 billion) writedown for Westinghouse, reviving concerns among investors that the value of assets and goodwill related to Westinghouse were overstated.

Nuclear power has become less popular since Toshiba's acquisition in 2006, especially in the aftermath of the Fukushima disaster which prompted many countries to freeze nuclear energy expansion plans.

The company said last November that such a writedown was not needed because the subsidiary was profitable, despite losses at parts of the operations in 2012 and 2013. A spokesman said on Friday that its last stress test conducted in January showed no need for a writedown.

But the spokesman confirmed several U.S. units have received a request for information from the U.S. Department of Justice and the Securities and Exchange Commission regarding accounting issues.

Bloomberg news agency reported a day earlier that U.S. authorities are opening a case on the conglomerate even though it had already been investigated in Japan, and could exert jurisdiction because the case involved U.S.-based Westinghouse.

Westinghouse denied its finances were under investigation.

"To our knowledge, Westinghouse financial reporting is not under investigation," Chief Executive Danny Roderick said in a statement.

Toshiba is due to brief reporters later in the day on its strategy for returning to profitability. It announced the sale of its medical equipment and home appliances units on Thursday, deals expected to help bolster its finances.