ABUJA (Reuters) - Anti-corruption group Transparency International said on Monday Nigeria’s government has in the run-up to elections expanded the use of opaque $670 million-a-year funds that fuel graft.

The funds, known as “security votes”, are a relic of military rule, mainly disbursed in hard cash and nominally released for dealing with unexpected security issues.

They come from both federal and state governments, although the vast majority is disbursed under the latter.

According to Transparency International’s report on Monday they have become “synonymous with official corruption and abuse of power”.

The watchdog’s report comes as President Muhammadu Buhari is gearing up to run for a second term in February 2019.

A Nigerian presidency spokesman did not respond to calls and messages seeking comment about the report.

Buhari has built his administration’s policy on the twin pillars of tackling Nigeria’s endemic corruption and restoring stability to the highly insecure country. Hundreds have died this year in communal unrest in the hinterlands and the Boko Haram Islamist insurgency in the northeast.

A number of former government officials have faced criminal charges related to alleged corruption since Buhari came to power. The opposition People’s Democratic Party, in power for 16 years prior to Buhari taking office in 2015, has accused the president of focusing on its members.

“The security vote is one of the most durable forms of corruption operating in Nigeria today,” said Katherine Dixon, Transparency International’s director for defense and security, in a statement.

“Yet instead of addressing its many urgent threats, the ever-increasing use of security votes is providing corrupt officials with an easy-to-use and entirely hidden slush fund.”

The group said the spending “is not subject to legislative oversight or independent audit because of its ostensibly sensitive nature”, adding that the funds are channeled into political activities such as election campaigns or embezzled outright.

It said federal-level total spending on items identified as security votes increased by 43 percent in 2018’s budget from 2017 and included payments to a university, a museum commission and a dental technology school.

Reuters checked some of the figures included in Transparency International’s report against a draft version of the 2018 budget, which has not yet been signed into law, and confirmed payments to those recipients were planned and identified as security votes.

Most of the estimated $670 million of security votes is disbursed by state governments, with federal spending making up only $51 million, Transparency International said. State government changes in disbursement varied, according to the report’s data.

Additionally, the largest security votes each year go to security agencies, and such spending under Buhari is less than under his predecessor, Goodluck Jonathan, the report acknowledged.

“Today, security votes are budgetary black boxes that are ripe for abuse by politicians seeking reelection or officials looking to run for political office,” Transparency International said.