Karzai said security forces in the south will be bolstered by new recruits from local tribes.
Karzai's comments come amid the biggest resurgence of the Taliban since their ouster from power in 2001.
More than 500 people, mostly militants, have been killed in the past three weeks, underscoring the threat to the country's future.
In the latest violence, the U.S. military says a U.S.-led coalition soldier was killed in a bomb attack in the southern province of Ghazni on June 11. The soldier, whose nationality has not been disclosed, was involved in operations against Taliban militants.
Overnight, gunmen killed four Afghan laborers in the south of the country. The government spokesman in Kandahar province, Daod Ahmadi, said the attackers stole $8,000. The four were driving home after weeks working for an Indian road construction company.
Ahmadi said it was not immediately clear whether the Taliban or ordinary criminals were responsible.