Seven US service members have died in one of the deadliest days for Americans in Afghanistan in recent months, as the Taliban continued attacks against foreign troops as part of their spring offensive.
Mr Karzai also said that talks on a US-Afghan bilateral security agreement to govern future American military presence in the country had been delayed because of conditions the Afghans were placing on the deal.
The US-led coalition reported that five international troops were killed by a roadside bomb in southern Afghanistan, and coalition spokesman Captain Luca Carniel confirmed that all five were American.
The coalition did not disclose the location of the roadside bombing. However, Javeed Faisal, a spokesman for the governor of Kandahar province, said the coalition patrol hit the bomb in the Maiwand district of the province, the spiritual birthplace of the Taliban.
Later, the coalition reported that a soldier with the Afghan National Army turned his weapon on coalition troops in the west, killing two in the most recent of so-called insider attacks. Such attacks by members of the Afghan security forces against their fellow colleagues or international troops have eroded confidence in the Afghan forces as they work to take over from foreign forces. Both killed were American, according to two US officials.
At the news conference, Mr Karzai said he had met earlier in the day with the Kabul station chief of the CIA and was reassured that the agency's payments to the Afghan government would continue. The New York Times had reported that for more than a decade, the CIA had given the Afghan National Security Council tens of millions of dollars in monthly payments delivered in suitcases, backpacks and plastic shopping bags.
Mr Karzai said he told the station chief: "'Because of all these rumours in the media, please do not cut all this money because we really need it. We want to continue this sort of assistance.' And he promised that they are not going to cut this money."
Mr Karzai described the payments as a form of "government-to-government" assistance, and while he wouldn't say how much the CIA gave to the National Directorate of Security, which is the Afghan intelligence service, he said the financial help was very useful. He claimed that much of the money was used to care for wounded employees of the NDS, Afghanistan's intelligence service, and operational expenses.
"We have spent it in different areas (and) solved lots of our problems," Mr Karzai said.