(Reuters) — Top insurers will have to hold more capital from 2019 to cover risks they pose to the financial system should they go bust, global regulators said on Thursday.

The announcement is a setback for a sector which argues that, unlike banks, it did not cause the financial crisis and should therefore not be tarred with the same regulatory brush.

Yet the reform was called for by world leaders in the Group of 20 top economies (G20), who have already approved a similar regime for 28 of the world's top banks, also by 2019.

The G20 argues the insurance sector poses just the same sort of potential systemic risks as do the banks. Problems at AIG in 2008 illustrated the threat, after the U.S.-based insurer had to be bailed out by the taxpayer in one of the biggest rescues mounted following the credit crunch.

Under the plans set out by the International Association of Insurance Supervisors (IAIS), insurers will be subject to tougher supervision and will have to show by 2015 how they can be wound up smoothly in a crisis, without relying on taxpayer bailouts, the body said in a statement.

A list of insurers coming under the scope of the new rules will be published later on Thursday. Reinsurers won't be named until July 2014 as more time is needed to analyze them.

Peter Braumueller, chairman of the IAIS executive committee, said the reforms had been tailored for insurers. Determining how much extra capital must be held will be done over two stages and will take several factors into account.

The IAIS will develop by the end of 2014 a basic "backstop" capital requirement for insurers deemed to be globally systemically important (GSIIs).

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A second stage will calculate a bespoke capital requirement based mainly on how much a company is plugged into the financial sector and if it has "non traditional" operations.

This refers to complex derivatives, extensive "repo" activities and securities lending, or if a company offers some types of annuities, mortgage insurance and credit guarantees.

Size alone and apparent global reach will only represent a small part of the capital calculation, the IAIS said.

Furthermore, insurers whose traditional lower-risk activities are clearly separated from riskier operations may not have to hold as much extra capital.

This will act as an incentive for some insurers to restructure themselves, seeking to apply lessons from the $85 billion rescue of AIG.

AIG's credit default swaps business, more traditionally a banking or hedge fund activity, turned sour in the financial crisis in 2008, leaving it open to huge liabilities.

The IAIS will come up with bespoke capital requirements for each GSII by the end of 2015, to be complied with from 2019.

The list of GSIIs will be updated by the G20's regulatory task force, the Financial Stability Board (FSB), every November. Insurers named in November 2017 will have to comply with the 2019 deadline for holding extra capital.

FSB Chairman Mark Carney has said that some insurers may not have to find extra capital as they will already hold enough to meet their GSII requirement.

The IAIS will also work on a "quantitative capital standard" for the insurance sector more broadly.