Anti-graft watchdog Transparency International warned that corruption is "undermining the rule of law" and "weakening democracy" in Malta in its annual report published Thursday.

The report accuses the Maltese government of "dragging its feet" in investigations into the murder of journalist Daphne Caruana Galizia.

Malta ranked in 50th place, one better than last year, but down 25 places since the country was first included in the report. With a score of 54, similar to last year's, Malta has seen a significant decline on the CPI, dropping six points since 2015.

The Corruption Perceptions Index (CPI) is a global ranking published by the NGO every January.

"In Malta, corruption is undermining the rule of law. A significant lack of political integrity contributes to politicians and others hiding illicit wealth behind secret companies," the report says.

"Given the “pair of political machines [that] have [for decades] operated with impunity on the island” it’s no wonder that two years after the assassination of journalist Daphne Caruana Galizia, who was killed while reporting on corruption, the country is still mired in corruption," it adds.

"Despite calls from Maltese citizens, Caruana Galizia’s family and the international community to solve the case, the government dragged its feet in the judicial procedures. Several scandals involving the Panama Papers, the collapse of a Maltese bank and the “golden visa” scheme that sells Maltese citizenship to wealthy overseas investors may also contribute to Malta’s decline on the CPI."

Denmark and New Zealand retained their place at the top of the index, which ranks 180 nations based on aggregated survey and assessment data from 13 different global institutions.

Western European and EU member states tended to score highest, while countries such as Somalia, South Sudan and Syria landed at the bottom of the rankings.

Yet TI warned western Europe against complacency, pointing out that even the high-scoring Nordic countries were implicated in transnational corruption scandals.

It also renewed its 2018 criticism of the USA, which ranked 23rd with its lowest score in eight years, saying that a "pay-to-play culture has only become more entrenched" during Donald Trump's presidency.

The report highlighted Angola as one of the countries which had improved its CPI score on 2018, noting that Isabel Dos Santos, the daughter of the former Angolan president, had been removed as head of the state oil and gas firm Sonagol in December.

Described as Africa's first female billionaire by Forbes magazine in 2013, Dos Santos is accused of "making a fortune at the expense of the Angolan people" in a report published Monday by the International Consortium of Investigative Journalists.

The report comes a day after the Economist Intelligence Unit’s annual index downgraded the state of Malta’s democracy the ‘flawed’ category.