Companies from Russia and China are seen as the worst offenders for paying bribes when doing business abroad, a new report said Wednesday, while Swiss and Dutch firms are the most honest.

Firms from China and Russia invested $120 billion (86 billion euros) abroad in 2010, Transparency International (TI) said, noting it was "of particular concern" that the two nations ranked in the bottom two.

"Given the increasing global presence of businesses from these countries, bribery and corruption are likely to have a substantial impact on the societies in which they operate," the Berlin-based non-governmental body said.

Companies' ability to compete fairly in these markets could also be affected, it warned.

Russian companies are increasingly present in the international oil and gas sector, while China is investing heavily in infrastructure and mining, especially in Africa, TI said.

Based on a scale of 0 to 10, where 10 signifies the view that companies from that country never bribe abroad, Russia was last with 6.1, while China scored 6.5.

The watchdog, which next month releases its main report on global corruption, said its Bribe Payers Index ranked 28 of the world's leading economies on the likelihood of their firms to bribe public officials abroad, based on a survey of 3,000 business executives.

Those surveyed reported that bribe-paying was to win public tenders, avoid regulation, speed up government processes or influence policy.

The countries were selected based on the value of their foreign direct investment outflows, the value of their exports and their regional significance, TI said.

Dutch and Swiss companies are considered least likely to bribe, both scoring 8.8, followed by those from Belgium, Germany and Japan. Britain ranks joint eighth place with Singapore and the United States is in tenth.

The index also ranked bribery within business sectors, placing public works contracts and construction companies last, while agriculture and light manufacturing are seen as the least bribery-prone sectors.

TI's chairwoman Huguette Labelle urged G20 governments meeting in Cannes from Thursday to urgently tackle foreign bribery.

"Governments can press home the advances made by putting resources behind investigations and prosecutions of foreign bribery so that there is a very real deterrent to unethical and illegal behaviour," she said in a written statement.

But the watchdog also warned that governments "must set an example" to companies by prohibiting corruption in the public sector.

It highlighted moves in both China and Russia to fight corruption.

Beijing passed an amendment, which took effect in May, making it a criminal offence for Chinese companies and nationals to bribe foreign government officials, adding, for the first time, an extra-territorial element, TI said.

Moscow, for its part, has been working with the Organisation for Economic Cooperation and Development to strengthen Russia's legal framework against bribery of foreign public officials, it said.

It also passed legislation in May criminalising foreign bribery for companies and individuals, it added.

TI releases its main annual corruption perceptions' report in December.