The mission is clear, but it's certainly not easy.

Whoever becomes the next governor of the Bank of Japan will be expected to make full use of the central bank's tools to reflate the Japanese economy, while avoiding accusations that it is igniting a currency war by deliberately depressing the yen.

Further aggressive easing of monetary policy in the world's third largest economy looks all but assured -- thanks to the early departure of the bank's current governor and a new prime minister with a strong mandate for bold action to stimulate growth.

Prime Minister Shinzo Abe is expected to name candidates for governor early next month, after Masaaki Shirakawa announced he would stand down on March 19, several weeks before his term was due to end.

Abe based his election campaign last year on a commitment to take radical steps to end years of deflation, combining promises of looser monetary policy with pledges of fiscal stimulus.

"Any Abe government pick for the Bank of Japan will move quickly after his confirmation with a more aggressive monetary policy in line with the government's wishes," analysts at the Eurasia Group wrote earlier this month.

Shirakawa agreed last month to double the bank's inflation target and adopt open-ended purchases of government bonds but is opposed to some of the more extreme proposals considered by the bank and has been accused of doing too little, too late.

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While a surprise candidate could still be put forward by Abe's Liberal Democratic Party, three frontrunners have emerged - Toshiro Muto, Kazumasa Iwata and Haruhiko Kuroda.

Kuroda, head of the Asian Development Bank, appears willing to follow through on Abe's plans, telling the Wall Street Journal this week that Japan has "plenty of room for monetary easing."

"If necessary and if appropriate, of course additional monetary easing this year could be justified," he said.

Muto and Iwata have been tipped by analysts at Citi as the favorites to replace Shirakawa.

Muto, chairman of the Daiwa Institute of Research and a former candidate for the governorship, would like the central bank to expand asset purchases. But he does not favor foreign bond purchases by the Bank of Japan, a move which could be viewed as a step too far by the country's trading partners.

Former deputy governor Iwata, however, may be prepared to buy foreign bonds in an effort to weaken the yen.

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The currency has already weakened significantly, falling almost 20% against the U.S. dollar since the beginning of October and driving up the stock market. It has also lost ground against the euro and some Asian peers, raising concerns that Japan may be engaged in a race to the bottom to promote exports.

Citi analysts believe the appointment of Muto or Iwata would further weaken the currency against the dollar -- to around 95 yen for Muto, and possibly as low as 100 yen should Iwata be chosen.

The political pressure on the Bank of Japan has caused consternation in the international community, with some lobbing charges of currency manipulation in Japan's direction.

Tokyo has rejected those claims, saying its policies are aimed at the economy not the yen, but the G7 group of leading industrial nations - including Japan - felt compelled to issue a rare statement earlier this week aimed at cooling talk of a currency war.

The statement reiterated the group's commitment to "market determined exchange rates" but within hours it was being interpreted as both supportive, and critical, of Japan's approach.

Finance ministers and central bankers from the larger G20 group will have another go at a meeting in Moscow starting later Friday.