OSLO – Norway’s massive sovereign wealth fund has increased its exposure to coal reserves even after imposing restrictions on investing in the fossil fuel that’s seen as one of the main catalysts for global warming, according to a report.

The findings are another illustration of how the ban, which restricts investments in companies that get more than 30% of their activity or revenue from coal, still allows investments in giants such as trader Glencore and miner BHP Group. Opposition politicians and environmental groups have called on Norway to close “loopholes” as the government prepares to present a review of the rules this year.

The Norwegian Parliament decided on the coal ban in 2015. Yet from the end of that year to the end of 2017, the fund’s share of reserves of mining companies that it was invested in rose by 10%, or 12% when adjusted for outflows, the UK non-profit InfluenceMap said in a report published on Wednesday.

The analysis also shows that the Norwegian fund has gone a long way in scrubbing itself of coal, mainly through divestment before Parliament imposed its restrictions. The fund’s reserves fell 63% over 2014 and 2015, while its coal intensity -- its reserves as a share of its assets -- is less than half the average of the world’s 60 000 largest listed funds.

The findings also don’t suggest the fund isn’t complying with the restrictions. Yet, it highlights that the ban still allows the fund to invest in some of the world’s biggest producers of coal since their output falls short of the 30% threshold, even if they exceed other miners or utilities in absolute terms.

The government should take note of the report, said Svein Roald Hansen, a representative for the opposition Labor Party, Parliament’s biggest group. Labor has advocated tightening the rules, but last year settled for a review. It will wait for the government’s analysis in the annual white paper due this spring before deciding on a way forward, Hansen said.

The Finance Ministry declined to comment on the report. The fund has said it will comply with whatever changes are made to the criteria.

“Our coal criteria is specifically worded to only include considerations of revenue or activity and not reserve numbers,” spokeswoman Marthe Skaar said in an email. “These numbers are not related to our coal criteria.”