(CNN) -- Afghanistan, North Korea and Somalia are seen as the most corrupt nations in the world, according to Transparency International's latest survey, released Tuesday.
More than two thirds of the 177 countries included in the 2013 Corruption Perceptions Index scored below 50, where 0 indicates the country's public sector is seen as highly corrupt and 100 as very clean.
Denmark and New Zealand performed best with scores of 91. Afghanistan, North Korea and Somalia tied last with 8 points each.
"All countries still face the threat of corruption at all levels of government, from the issuing of local permits to the enforcement of laws and regulations," said Huguette Labelle, Transparency International's Chair in a statement.
In Syria, where 100,000 have died in a conflict which began in 2011 and has now exploded into war, people regard its public sector as increasingly corrupt.
The stricken nation dropped 9 points from 144th place to 168th. Libya, Yemen, Spain, Australia, Guatemala and Madagascar were among the other countries whose scores declined significantly.
Myanmar saw the biggest improvement, rising from 5th last position in 2012 to 19 places from the bottom this year.
The change reflects the benefits of introducing more open and democratic rules after years of military rule, according to Transparency International's Asia Pacific Director, Srirak Plipat.
Myanmar also ratified an international treaty against corruption in December 2012 and the parliament approved an anti-corruption law in July, although this is yet to come into force.
While Greece's score rose four points this year to 40, but remained the lowest ranking country in the European Union in 80th place. Brunei, Laos, Senegal, Nepal, Estonia, Lesotho and Latvia also improved.
The UK jumped from 17th to 14th place with a score of 76, two points up from last year. The U.S. did not change from last year, ranking 19th with a score of 73. China's rank did not change. Australia dropped two places to 9th position with a score of 81.
The Corruption Perceptions Index is based on perceptions of corruption in public institutions like political parties, police and justice systems according to experts and business people.
Strong access to information systems and rules governing the behavior of public officials can help a country improve, while a lack of accountability and weak public institutions damages these perceptions, Transparency International said.
The organization called on public institutions and officials to be more open, adding that corruption remains notoriously difficult to investigate and prosecute.