KABUL - Afghan President Hamid Karzai vowed Tuesday that his new government would eradicate corruption and unite the country after months of political chaos as he offered an olive branch to Taliban insurgents.

Under pressure from US President Barack Obama to wipe out corruption after turbulent election process steeped in fraud, Karzai used his first appearance since electoral authorities declared him president to pledge a cleaner rule.

"Afghanistan's image has been tainted by corruption. Our government's image has been tainted by corruption," Karzai told a press conference flanked by vice president Mohammad Qasim Fahim, who is widely accused of rights abuses.

"We will strive, by any means possible, to eradicate this stain."

Karzai was declared president for another five years after the election commission, whose chief he appointed, cancelled a run-off ballot following the withdrawal of his only challenger, Abdullah Abdullah.

Karzai has been urged by a number of world leaders to ensure his next government can command the support of all Afghans as Obama mulls whether to pour tens of thousands more US troops into battle against the Taliban.

"The future government will be a government that reflects all the people of Afghanistan... We hope that no-one feels themselves isolated from this future government," he said.

The 51-year-old president, whose warm relations with the West have cooled over corruption and spiralling insecurity, also urged his Taliban "brothers" "to come home and embrace their land".