Media playback is unsupported on your device Media caption Shinzo Abe: "This is going to be a good cycle to be felt by our people"

Japanese PM Shinzo Abe says his win in Sunday's upper house elections will help him form a stable cabinet, ending political volatility.

Exit polls suggest his ruling coalition won at least 76 of the 121 seats contested, broadcaster NHK says.

This would give Mr Abe control of both houses of parliament - a first for a prime minister in six years.

Mr Abe said the result was an endorsement of his more conservative economic and political reforms.

"We have received overwhelming support from the people for our policies of improving the economy, and solid and stable politics," Mr Abe told reporters after Sunday's vote.

The deadlock in parliament has been seen as a key factor in Japan's recent "revolving door" of prime ministers.

'Twisted parliament'

Analysis In foreign policy, Japan's immediate neighbours, most notably South Korea and China, worry that the prime minister may be planning to pursue an aggressively nationalist agenda, encompassing wartime historical revisionism, the abandonment of Article 9 (the so-called "peace clause" of Japan's constitution), and a more belligerent defence of Japan's territorial interests in the East China Sea and the Sea of Japan. The reality is likely to be more prosaic and less dramatic. Abe's public rhetoric over contentious wartime issues can at times be insensitive and diplomatically ill-judged, and there is no mistaking the prime minister's personal desire to promote constitutional revision. However, Japan's public remains largely evenly divided about the merits of re-visiting such contentious subjects and, notwithstanding the LDP's rising political fortunes, the government still lacks the necessary two-thirds majority in the Upper House to effect constitutional revision. What Abe's win means

Half of the seats in the upper house were being contested in Sunday's election.

Official results are not expected until later on Monday, but exit polls suggest Mr Abe's Liberal Democratic Party (LDP) and its junior partner New Komeito will now control 135 seats in the 242-seat upper house, NHK reports, giving the coalition a comfortable majority.

The main opposition party, the Democratic Party of Japan (DPJ), was expected to win 17 seats, in its worst showing in 15 years, NHK said.

Japan's upper chamber, while not as powerful as the lower house, is able to block legislation introduced by the government.

In recent years opposition parties have had enough combined seats to control the chamber, leading to what has become known as a "twisted parliament".

This has resulted in factionalism and multiple changes of prime minister - Japan has had six in the last six years.

As first election results began emerging, Mr Abe said many voters believed in his party's economic policies which were having a positive impact.

"These policies are contributing to the economy already and further improvement is needed, including wage increases, more consumption, more investments.

"I want to make a virtuous cycle of improving the employment situation, increasing salaries and bringing about a rise in corporate investment.

Structural change

Mr Abe, 58, has relatively strong public support for his proposals for economic reform - the so-called "Abenomics" - which seek to revive the economy, stagnant for two decades.

Since his government came to power, the economy has grown by 4% and the stock market by more than 40%.

His first two measures - the "arrows" - involved a big injection of cash by the Bank of Japan and a major boost in government spending.

Media playback is unsupported on your device Media caption Rupert Wingfield-Hayes reports on celebrations in Japan, and the road ahead

But he now faces the task of driving through difficult structural changes to the economy. Trade barriers need to come down, taxes will need to rise and large parts of the economy will have to be deregulated.

One of the decisions he will have to make later this year is whether to raise sales tax next April from 5% to 8% to help reduce Japan's national debt.

Mr Abe is also considering whether to cut Japan's 36% corporate tax to spur growth and open up the power industry, currently controlled by regional monopolies.

And his government is keen to join a free trade agreement known as the Trans-Pacific Partnership (TPP), being negotiated by 11 countries.

Mr Abe is also thought likely to endorse several controversial policies beyond the economy. These include restarting Japan's nuclear reactors - something many in Japan are opposed to.

In the long-term, some believe he may be eyeing revision of Japan's pacifist constitution, including a section which prohibits the use of force in international disputes except for self-defence.

But correspondents say pursuing nationalistic policies may cause tension with neighbouring countries.

Speaking to NHK after his win, Mr Abe said he wanted to "expand and deepen" debate over the constitution, comments echoed by his top government spokesman, Chief Cabinet Secretary Yoshihide Suga.

"We have sought to revise the constitution in order to have one of our own. We have finally come to a point where a revision is a realistic option," he said.

"We would definitely want to deepen a discussion."

Poll figures, however, show that the Japanese public remains more interested in economic issues than in the potentially divisive issue of constitutional change.