WASHINGTON (Reuters) - Cindy Sheehan, who became a leading anti-war activist after her son died in Iraq, said on Monday she will run against House of Representatives Speaker Nancy Pelosi if the Democratic leader fails to seek the ouster of President George W. Bush within the next two weeks.

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The 49-year-old, whose soldier son Casey died in combat in Iraq in 2004, told Reuters she would run for Pelosi’s house seat in 2008 if the California Democrat fails to endorse impeachment proceedings against Bush and Vice President Dick Cheney by July 23.

That is the date when Sheehan and a group of supporters are due to arrive in Washington as part of a cross-country caravan and walking trip for humanity, set to begin from Bush’s hometown of Crawford, Texas, on Tuesday.

“If Nancy Pelosi doesn’t support articles of impeachment ... by the time we get there, then I will announce my candidacy against her,” she said in a telephone interview from Crawford.

Sheehan said Bush and Cheney should be impeached for lying to the American people about Iraq and anti-terrorism policies that she believes violate U.S. law and international treaties banning torture.

“In November ‘06, Americans went to the polls to vote for change and what we’ve gotten in the last six months since the Democrats have been in control of Congress is more politics as usual,” she said.

Pelosi spokesman Brendan Daly said in a statement that the Democratic leader is focused on ending the war. “She believes that the best way to support our troops in Iraq is to bring them home safely and soon,” the statement said.

Sheehan, who has never held public office, is also encouraging others to challenge Democratic incumbents.

Sheehan gained prominence as an anti-war activist in 2005 when, as the mother of a dead soldier, she said she wanted to meet with Bush as he vacationed at his ranch in Crawford.

She announced in May that she would end her public role in the anti-war movement, saying she had reached the conclusion that her son “did indeed die for nothing” and was “killed by his own country which is beholden to and run by a war machine that even controls what we think.”

A California resident, Sheehan said she would run as an independent in Pelosi’s northern California congressional district, which is centered in San Francisco.