A US congressional watchdog has found no evidence that a 2012 Securities and Exchange Commission (SEC) conflict minerals disclosure rule has reduced violence in Democratic Republic of Congo (DRC), it said in a report on Monday.

Armed groups continue to fight for control of gold mines in the east of the Central African country, the US Government Accountability Office (GAO) said in its report.

It also said the rule - which requires some companies to report on their use of tantalum, tin, tungsten and gold - has likely had no effect in neighbouring countries.

"GAO found no empirical evidence that the rule has decreased the occurrence or level of violence in the eastern DRC, where many mines and armed groups are located," the report said.

"GAO also found the rule was associated with a spread of violence, particularly around informal, small-scale gold mining sites," it said, adding that gold is the most difficult to trace, and easiest to smuggle, of the four minerals covered by the rule.

Congo is the world's top producer of tantalum, which is considered a critical mineral by the US and the European Union.

The report added that "the SEC disagreed with some of GAO's findings and raised concerns about some of its methodology and analyses." The GAO said it made certain adjustments that did not materially affect its findings.

The SEC did not immediately reply to a request for comment.

Last year, GAO said that some US companies buying minerals from Congo and its neighbours were failing to meet disclosure requirements.

On September 30, Bintou Keita, head of the United Nations (UN) mission in Congo, told the UN Security Council that M23 rebels in the east are generating $300 000 per month in revenues in a coltan-mining region they seized earlier this year.