WASHINGTON, District of Columbia (AFP) - The United States (US) was upbeat Monday about possible economic reforms in Japan after an election win by Prime Minister Shinzo Abe's party but cautioned against steps that would increase regional tension.

Mr Abe's Liberal Democratic Party and its partner New Komeito on Sunday retook control of the upper house, ending an era of divided parliaments that has hampered legislation and helped bring down six short-lived premiers.

"If this is a step that will help facilitate greater continuity of leadership in Japan, I think it will be welcome(d) by all of Japan's friends," said Mr Danny Russel, the US assistant secretary of state for East Asia.

Mr Russel, a Japan specialist who took over the top Asia job last week, told reporters that President Barack Obama supported Mr Abe's goal of reforms aimed at rejuvenating the world's third largest economy.

"Certainly with the mandate that he has won, we watch with hope and encouragement as he approaches that objective," Mr Russel said.

"A thriving Japanese economy isn't only good for the people of Japan, it's good for the region and certainly it's good for the United States," he said.

Mr Abe plans to meet on Friday in Singapore with US Vice-President Joe Biden after the Japanese leader stops in Malaysia to enter negotiations on the Trans-Pacific Partnership, a US-backed free trade pact.

Mr Abe has vowed a firm line on China, which has increasingly sent ships to contested waters, and moved to step up officially pacifist Japan's defence spending.

But since returning his party to power in December, Mr Abe has focused on the economy and mostly played down his conservative and often controversial views on war history that have irked China, South Korea and US lawmakers.

Mr Russel carefully avoided direct criticism of leaders in the region but renewed US calls for lower tension.

"It's hugely important that the relations between Japan and its neighbors improve, that problems be dealt with in a peaceful and a thoughtful way," Mr Russel said.

"We hope that all leaders and the publics will be guided by a sense of wisdom and shared interest and will take actions and decisions with a view to the future," he said.

He reiterated that the US does not take a position on sovereignty claims but sought "peaceful and responsible management" of disputes.