KABUL (Reuters) - Dozens of Afghan political parties launched a new coalition bloc on Thursday hoping to pose a stronger challenge to the government of President Hamid Karzai, which they say is corrupt and misuses funds meant to rebuild their war-torn state.

In a room packed with hundreds of representatives from Afghanistan's provinces and ethnic groups, speakers said the bloc had secured enough support, including from a number of MPs, to provide a real counterweight to Karzai.

Karzai has ruled since soon after the Taliban government was toppled by U.S-backed Afghan forces in late 2001, but his grip on power has come under increasing pressure since a fraud-marred presidential election in 2009.

The National Coalition of Afghanistan, led by Abdullah Abdullah, an ophthalmologist who was Karzai's main rival in the 2009 vote, said the government had done little to rebuild the economy, erect infrastructure and bring people out of endemic poverty during Karzai's 10 years running the country.

Thousands of lives and billions of dollars have failed to secure Afghanistan and only fragile gains have been made in education and women's rights, falling well short of promises made a decade ago.

"We don't have any enmity with our friends who lead the country, but they have lost their way. Afghanistan's people are supporting the government but the gap between people and the government is growing day by day," Abdullah told the crowd.

The political battle has been undermining international efforts to foster good governance, particularly as the West starts handing over control of security to Afghan forces.

The NATO-led force in Afghanistan, which stands at about 130,000, is due to withdraw the last of its combat troops by the end of 2014.

Political parties in Afghanistan rarely have the structure or discipline of parties in Western political systems. The new coalition is meant to present a joint opposition ahead of the next presidential vote, also due in 2014.

The bloc called for a more decentralized political system, with proper checks and balances, so the fate of the country is not dictated by a political elite. It also questioned Karzai's desire to negotiate a peace deal with the Taliban.

One speaker accused Karzai of luring opposition members with money or government positions to sustain their support.

The bloc also accused Karzai of planning to change the constitution to be able to run for a third term in power when his current five-year term ends, an allegation the president has so far denied.

"Ten years for a president of a country is enough time. When will you stop corruption, stop the mafia?" said Humayun Shah Asifi, a 2004 presidential candidate.

(Reporting by Agnieszka Flak and Mirwais Harooni; Editing by Sanjeev Miglani)