Afghanistan set a 9 October date for presidential elections, but delayed more complicated parliamentary polls until spring 2005, as the government struggles to maintain calm.
The report stated that the increasingly tense security situation in which the elections are taking place is a growing concern.
Recent incidents suggest violence has "increased in frequency and escalated in gravity," the UN said in a report on the development of Afghanistan's political rights, released on Saturday.
National security forces, election and government officials, and local and international aid workers have been the main targets of these incidents, the report added.
Growing death toll
An Afghan working on a road building project in southern Zabul province for USAID was killed Friday and two of his colleagues were wounded.
The latest incident follows a bomb blast a week earlier in the western city of Herat, which killed six people and wounded more than 30.
Arnault said the violence "continues to play a great limitation on the possibility of political expression,".
In Zabul province only 12% of the population are on the voter's roll.
The security situation in southern Zabul and Uruzgan provinces make political freedom similarly difficult, the report explained.
In Herat, Ismail Khan, who controls the city, has squashed any political opposition and rules the airwaves and the press, the report claimed.
"According to political party representatives, there is little hope that government controlled Herat television would be accessible for campaign purposes for non-state political actors," it added.
President Hamid Karzai last week described the current situation of instability by the different groups as a bigger threat to stability than the Taliban insurgency and said disarmament was vital to secure Afghanistan's political future.
Afghans have been braving violent
outbreaks to register to vote
So far, just more than 10,000 of an estimated 60,000 men have laid down their guns, although the goal is to disarm 37,000 in time for spring parliamentary elections.
Despite security risks Afghans are registering to vote, with 7.4 million of Afghanistan's 10.5 million eligible voters having put their names on electoral lists by Friday.
Arnault also sounded an upbeat note, describing the embryonic political parties in some parts of the country as "encouraging".
In northern Khost and Jalalabad provinces there is an "emergence of a fairly vibrant political life, with a number of political parties which two years ago would not have operated openly, but begin today to express their opinion and organize themselves," he said.