TOKYO (REUTERS) - The Bank of Japan announced on Tuesday its most determined effort yet to end years of economic stagnation, saying it would switch to an open-ended commitment to buying assets next year and doubling its inflation target to 2 per cent.

It promised to reach the inflation goal "at the earliest possible time."

The steps mark a break with an earlier policy of topping up a lending and asset buying programme launched in October 2010 and follow weeks of relentless pressure from new Prime Minister Shinzo Abe for a greater push to beat deflation and lift the economy out of recession.

In a joint statement with the government, it affirmed a well-flagged move to commit to the inflation target. Consumer price inflation has reached 2 per cent in only a handful of months since the late 1990s.

But aware that markets had already factored in the new price goal and more asset buying and that merely meeting those expectations could trigger a negative reaction, central bankers took steps that several analysts thought would only come later.

"This is very good news. For once, the BOJ has been more aggressive than the market expected," said Mr Brian Redican, senior economist at Macquarie in Sydney. "The government is clearly forcing the pace of change, which is no bad thing."

The central bank said that from 2014 it would switch to an open-ended approach of buying a certain amount of assets - 13 trillion yen (S$178 billion))- each month without setting a deadline for completing the purchases.

The yen, which inched up ahead of the policy announcements, fell immediately after the decision, though later crept up higher.

Several analysts pointed out, however, the BOJ could have done even more and there will be expectations that it will follow through with further steps mooted by politicians, economists and some central bank policymakers.

One such step would be to scrap the 0.1 per cent floor for short-term interest rates, while another would be for the central bank to buy longer-duration bonds.

"There's still a lot of work to do, and still a lot of room for improvement," said Mr Tadashi Matsukawa, head of fixed income at Pinebridge Investments in Tokyo.

Mr Abe, who led his Liberal Democratic Party to a landslide victory in a Dec 16 parliamentary election, made promises of aggressive budget and monetary stimulus a centrepiece of his campaign.

His pledges to boost public spending and repeated calls for more BOJ action helped reverse a long-term rise in the yen and set off a stock market rally led by exporters and construction firms.

But many economists have warned the stimulus could give the sluggish economy only a temporary jolt if the government fails to follow through with politically more difficult economic reforms such as deregulating its protected farming sector.

They also warn that the push to reflate the economy could backfire if Abe's government fails to convince markets that it has a credible plan to get Japan's ballooning debt back under control.

Seeking to address such concerns, the government said in the joint statement it would draw up a growth strategy and pursue structural reforms to help Japan escape deflation and pledged to maintain fiscal discipline. Economics Minister Akira Amari attended the BOJ meeting to represent the government's views.

The yen has lost 13 per cent against the dollar in the past two months to hit a two-and-a-half-year low on expectations of bolder central bank action. Tokyo stocks have gained a fifth on the view the weaker yen will boost the export earnings of the likes of Nissan Motor Co and Canon Inc.

The yen's declines, however, have drawn complaints from countries like Russia and Germany, worried that it could set off destabilising currency devaluations.

In a sobering reminder that Japan still faced an uphill battle in pulling out of more than a decade of low-grade deflation, the BOJ's updated economic forecasts showed core consumer prices inching down in the current fiscal year and up only 0.9 per cent in the fiscal year ending in March 2015.

"Headline says core inflation at only 0.9 per cent in 2014 so when will they meet their inflation target of 2 per cent?" asked Mr Joseph Capurso, currency strategist at Commonwealth Bank Of Australia in Sydney.