By Madeline Chambers

BERLIN (Reuters) - The German government was criticized on Wednesday for overseeing a doubling of arms exports last year which detractors say shows a two-year-old policy aimed at curbing sales of weapons to volatile regions has failed.

Chancellor Angela Merkel's cabinet approved the economy ministry's annual arms report, which confirmed figures leaked over the weekend that the government waved through 7.86 billion euros worth of sales in 2015, twice the previous year's level.

The main target of criticism was Sigmar Gabriel, the Social Democrat (SPD) economy minister who made much of bringing in tighter rules in 2014 to limit arms sales to the Middle East and in particular states such as Qatar and Saudi Arabia.

In the report, Gabriel's ministry pointed to several big one-off sales, including a 1.6 billion euro sale to Qatar of fighter tanks and tank howitzers and accompanying parts.

"Sigmar Gabriel has broken his promise to better control arms exports," said Jan van Aken of the radical Left party.

Renke Brahms of the EKD Evangelical Church council said the numbers were a "scandal", homing in on sales to Saudi and Qatar.

"The human rights situation in these Arab countries is bad and Saudi Arabia contributes to a lack of peace in the Gulf region," said Brahms.

Some 41 percent of sales went to EU or NATO states, such as a 1.1 billion euro sale of refueling aircraft to Britain.

After Qatar and Britain, the biggest buyers were South Korea, Israel and the United States. Also in the top 15 were Algeria, Saudi Arabia, India, Russia and Kuwait.

Gabriel, the favorite to stand against Merkel in next year's election, has said the rise is largely due to contracts approved by Merkel's previous center-right coalition.

But the ministry has also said arms exports rose to 4.03 billion euros in the first half of this year and German media reported that Gabriel had just approved a further 10 arms export projects, including to Saudi Arabia, Pakistan, Egypt and Mexico.

Selling weapons is highly sensitive in Germany due to the country's military and Nazi past. It is the world's fifth biggest exporter of major arms, according to the SIPRI research institute, and the industry employs about 80,000 people.

Gabriel pointed out that approvals for small arms fell to 32.4 million euros from 47.4 million euros in the previous year. "These weapons are especially dangerous as they are the weapons of civil wars," Gabriel told the Sueddeutsche daily on Monday.

(Reporting by Madeline Chambers; Editing by Catherine Evans)