Britain does not believe the Afghan government it backs is taking the fight against corruption as seriously as it should, and future aid could be linked to anti-graft progress, a British minister said on Thursday.

After a decade of war and billions of dollars in aid, corruption in Afghanistan is rampant and violence is spreading even into once-peaceful areas as Western forces begin to draw down combat troops ahead of an end-2014 pullout.

We're not at all convinced at the moment that it has the priority we think it should and accordingly we're getting that message out loud and clear, Foreign Office Minister Alistair Burt told reporters in the Afghan capital.

(Corruption) is well up the scale of international concerns and we're very conscious that it's not something that can be dealt with immediately, he said. This is not easily dealt with but some realistic sign that it's taken very seriously ... is very important.

Graft is common at all levels of Afghan society. A survey by watchdog Transparency International rated Afghanistan as one of the world's most corrupt countries, ranked equally with Myanmar, and only slightly cleaner than North Korea and Somalia.

London is the world's fourth-largest donor to Afghanistan.

Britain's aid watchdog said this month it must tighten oversight of its aid programme to Afghanistan, worth hundreds of millions of pounds a year, to lessen the risk of losing the money to theft, fraud or corruption.

Afghanistan relies on foreign aid for the bulk of its spending, but many international donors say they are reluctant to channel aid through the country's ministries partly because they fear it could be lost to corruption.

In a major recent scandal, lender Kabulbank gave out hundreds of millions of dollars in unsecured and undocumented loans to Afghanistan's elite, including sitting ministers and an ex-warlord, before the discovery of the fraud in 2010.

Western officials described the bank as a Ponzi scheme.

We're raising our voice on the issue (of corruption), Burt said. Kabulbank stands out as a symbol of concern where everybody appears to know what has happened but the most effective action taken has yet to be seen.

Britain will pull out 500 soldiers from Afghanistan this year, and the remaining 9,000 will be brought home before the end of 2014.

Britain's outgoing ambassador to Kabul said in a newspaper interview earlier this month that Afghanistan's government must take decisive action against corruption, or face the possible withdrawal of British funding for its security forces.

Burt also hinted that further British aid could be dependent on gains the Afghan government makes in the fight against corruption.

There was a link between the long-term commitments that could be made at a major conference about Afghanistan in Tokyo in July, and the international community's level of confidence in how money would be handled, he said.

Good signals from the top about how corruption is to be dealt with will be important, Burt said.

(Reporting by Jack Kimball; Editing by Daniel Magnowski)