Transparency International (TI) says government crackdowns on NGOs and media are associated with higher levels of corruption and most countries are "moving too slowly" to combat graft.
More than two-thirds of the 180 countries on the Berlin-based watchdog's Corruption Perceptions Index 2017 scored below 50 on a scale ranging from zero, perceived to be highly corrupt, to 100, perceived to be very clean.
The average score on the index, which ranks countries and territories by their perceived levels of public-sector corruption according to experts and businesspeople, was 43.
"Despite attempts to combat corruption around the world, the majority of countries are moving too slowly in their efforts," the anticorruption group said in a statement released along with the index on February 21.
"While stemming the tide against corruption takes time, in the last six years many countries have still made little to no progress," TI said.
"Even more alarming, further analysis of the index results indicates that countries with the lowest protections for press and nongovernmental organizations also tend to have the worst rates of corruption," it said.
Not Getting Better
The new index indicates that Afghanistan remains one of the most corrupt countries in the world and has failed to make progress in tackling graft over the past year.
It scored just 15, unchanged from the previous year, with its ranking falling to 177 in the index from 169 in 2016.
TI said New Zealand and Denmark ranked the cleanest, with scores of 89 and 88 respectively, while Syria, South Sudan, and Somalia were at the bottom, with scores of 14, 12, and nine.
The best performing region was Western Europe, with an average score of 66. The worst performing regions are Sub-Saharan Africa, with an average of 32, and Eastern Europe and Central Asia, with an average of 34.
Several former Soviet republics ranked poorly, with Uzbekistan at 157, Tajikistan at 161, and Turkmenistan at 167, the index showed.
Russia's score remained unchanged from the previous year at 29, ranking it 135th of the 180 countries surveyed -- the same as Kyrgyzstan.
In the former Soviet Union, Georgia ranked 46th with a score of 56; Belarus ranked 68th with 44; Armenia ranked 107th with 35; Azerbaijan, Kazakhstan, and Moldova ranked 122nd with 31; and Ukraine ranked 130th with 30.
In the Balkans, Montenegro ranked 64th with a score of 46; Serbia ranked 77th with 41; Kosovo ranked 85th with 39; Bosnia-Herzegovina ranked 91st with 38; and Macedonia ranked 107th with 35.
Pakistan ranked 117th with a score of 32, while Iran ranked 130th with 30.
The United States ranked 16th, up from 18th in the 2016 index, with its perceived corruption score improving by one point to 75.