President Hamid Karzai moved Saturday to replace a powerful governor and militia leader who has long defied his authority and held near-total sway over one of the country's wealthiest regions.

The decision to remove Gov. Ismail Khan of Herat, which U.S. diplomats here helped engineer, came after recurrent clashes between regional militias left the once-untouchable Khan politically weakened.

The Kabul government said Khan would become minister of mines and industry in the national government, but Khan told news agencies that he would not, and that he preferred to remain in his home region. He said he was a "military man, not an engineer," and that such a change would not help stabilize the country with elections approaching on Oct. 9.

Diplomats and Afghan defense officials said extra contingents of national army troops and police, as well as a large delegation from the Defense Ministry, were on their way to Herat to maintain security. They said Sayeed Mohammed Khairkhwa, currently Afghan ambassador to Ukraine, would be sent Sunday to replace Khan as governor of Herat, an isolated but strategic province near the border with Iran.

American diplomats confirmed Saturday evening that Khan had turned down Karzai's offer to join the government in Kabul, but they said he had agreed to become a "private citizen" in Herat, which he has ruled as a religious fiefdom since the fall of the Islamic Taliban administration in late 2001.

The firing was announced on the day that Karzai formally launched his campaign for the presidential election. In a speech, he promised to improve the country's security and standard of living, but said he would not form a coalition government with his political or ethnic rivals.

Khan controls a sizable contingent of troops from his days as an anti-Soviet fighter. He is admired by many Afghans as a religious leader and has won considerable local support by spending large sums of money from border revenues on public works, including schools, clinics, roads and parks.

"This is a very substantial development in post-Taliban Afghanistan," one U.S. diplomat said. He noted that "national government authority is getting extended in a significant and dramatic way" to an area controlled by one of the country's strongest and most resistant regional leaders.

Jean Arnault, the U.N. special representative in Afghanistan, said the world body welcomed Karzai's decision. He called the move "an opportunity to prevent further fighting, to reassure the population and to ensure the peaceful preparation of the upcoming presidential election" in a troubled area of the country.

Khan's removal is the second such action recently by Karzai, who has often been criticized for negotiating and compromising with defiant ethnic warlords instead of putting them in their place. In late July, he unexpectedly dropped Mohammed Fahim, another powerful militia leader and the defense minister, from his campaign ticket as first vice president.

Several other major militia leaders have either joined the government recently or have decided to challenge Karzai for the presidency, raising hopes for a peaceful election. On the other hand, most militia leaders, including Khan, have resisted a national plan to disarm and demobilize their forces.

In public statements Saturday, Karzai and U.S. envoy Zalmay Khalilzad couched Khan's removal in flowery, face-saving language. Karzai's office praised his "invaluable commitment and efforts" as governor, and said his skills "must be utilized" nationally. Khalilzad said Khan has "done a great deal for Afghanistan" and can continue his "tradition of public service" in Kabul.

One U.S. diplomat said Khan should take on a new role as an informal elder statesman, and that as Afghan democracy evolves, "there should be a way for former governors, presidents, ministers to lead a very respectable life, to be consulted instead of persecuted."

But beneath the diplomatic veneer, the removal of Khan appeared closer to a carefully orchestrated coup. Though roles played by various groups and individuals remain murky, Afghan and U.S. officials appear to have moved to capitalize on a bout of regional bloodletting to push Khan out.

In mid-August, Herat was nearly overrun in an attack led by militia leader Amanullah Khan, a rival to Ismail Khan. The assault was repelled by Afghan national troops and a truce was brokered with American assistance. Amanullah Khan was brought to Kabul and placed under house arrest; there have since been reports that his men beheaded and skinned some of Ismail Khan's troops.

There have also been persistent reports that several officials in Karzai's government were involved in organizing the attack, which was joined by several other regional rivals of Ismail Khan and left the once-invincible leader shaken and vulnerable.

Once the military situation stabilized, U.S. diplomats put increasing pressure on Khan to step down, telling several journalists two weeks ago that his days as governor were numbered. The only question, they said at the time, was whether he would leave before or after the presidential election.

Ismail Khan, above, turned down a bid from Afghan President Hamid Karzai, right, to join the national cabinet. U.S. diplomats aided in Khan's removal as governor of Herat.