Aso will face off against former Cabinet secretary Yasuo Fukuda in the Liberal Democratic Party's leadership race. The leader of the party, which controls parliament's lower house, is guaranteed election to the post of prime minister.
Shinzo Abe unexpectedly announced his resignation as premier on September 12, saying a change of leadership was needed to garner public support for government policies. Abe, 52, was later hospitalized, suffering stress and exhaustion.
Yasuo Fukuda, 71, is seen as the frontrunner in the contest for premier, with the backing of key politicians in the ruling party, and slightly stronger support among voters.
Abe announced his resignation following a difficult year-long premiership, with an upper house election defeat and mounting controversy over his country's support for U.S.-led military operations in Afghanistan. He said a change of leadership was needed to push forward with Japan's involvement in counterterrorism efforts.
Taro Aso, 66, a key ally of Abe, shares the ex-premier's patriotic values and hawkish stance on security issues.
The Democratic Party has pledged to vote against Japan's continued support for the United States-led coalition in war-torn Afghanistan.
Japanese refueling supply ships and Maritime Self Defense Force destroyers have been based in the Indian Ocean since November 2001 to support coalition efforts in Afghanistan, following the signing of the antiterrorism law in 2001, which has been repeatedly extended. The law is set to expire November 1, and opposition forces are against prolonging it.
On July 29, the ruling coalition led by the Liberal Democratic Party lost its majority in the upper house of parliament following a major public scandal in which millions of pension records were lost.
In March 2007 Shinzo Abe, widely considered a nationalist, sparked controversy in Asia and the West by playing down Japanese war crimes in WWII, and claiming there was no evidence that Japan's army abducted around 200,000 young women during the war from Korea, China, and other occupied territories, for use as sex slaves.
