Prime Minister Yoshiro Mori's grip on power further weakened Thursday as a key member of a Liberal Democratic Party faction supporting him said he should voluntarily step down after the fiscal 2001 budget clears the Diet in late March or April.

Former Foreign Minister Kabun Muto told a group of reporters that Mori "was acceptable" up until the budget clears the legislature but that it is best for the prime minister to then voluntarily resign.

Muto is a senior member of the LDP faction that is co-led by Takami Eto, former head of the Management and Coordination Agency, and Shizuka Kamei, LDP policy affairs chief.

The Eto-Kamei group had been remaining behind Mori, although the largest LDP faction -- headed by Ryutaro Hashimoto, state minister in charge of administrative reform -- has in recent days distanced itself from the embattled prime minister.

With the Eto-Kamei group beginning to give Mori the cold shoulder, the prime minister's support base within the LDP has basically dwindled to his faction alone.

Mori, whose popularity rating has fallen below 10 percent, has seen support within his ruling triumvirate dissipate after it was learned this month that he continued to play golf despite receiving word that a fisheries training vessel sunk off Hawaii after being hit by a U.S. Navy submarine.

New Komeito, a key partner in the ruling coalition, has called on the LDP to take action to remove Mori, and senior LDP officials are mulling when the prime minister should step down.

Mori, however, has so far indicated that he is determined to cling to power.