However, Kubis said he was encouraged by the work being done by the Afghan government, the election commission, civil society institutions and political forces to ensure the 2014 presidential election is free and fair.
The constitution bars Afghan President Hamid Karzai from running for a third term.
"We have no other intention but to support a good, democratic election in this country, including financial support," Kubis said, adding that it's still unclear how much money the international community will pledge to support the election.
Elsewhere in Afghanistan, clashes broke out between Taliban fighters and Afghan policemen in Archi district of Kunduz province in the north. Four policemen were killed, said provincial police spokesman Sarwar Hussaini.
The number of casualties among Afghan security forces has been on the rise as international forces draw down in numbers and the Afghan troops shift into a more frontline role in the war against the Taliban and other insurgent groups.
Civilians have also continued to suffer heavy casualties from bombings and targeted killings.