Germany's health minister came under the spotlight Sunday over reports that his husband's company sold masks to the ministry, as a row over mask contracts dogging Chancellor Angela Merkel's conservatives refused to die down.

Spiegel Online reported that the health ministry run by Jens Spahn bought 570,000 masks from a company called Burda last year.

Spahn's husband, Daniel Funke, runs Burda's Berlin office.

A spokesman from Burda told Spiegel that the company had helped to procure masks in April last year, when governments across the world were desperately scrambling to get hold of the mouth and nose covering.

The spokesman added that Funke was neither involved nor implicated in the deal.

Contacted by AFP, a health ministry spokesman said the contract with Burda "was concluded and carried out after the reception of offers in a standardised process at market prices".

The report came as several MPs in Merkel's CDU party and Bavarian sister party CSU were hit by a series of damaging graft allegations just six months ahead of general elections.

Bavaria's former justice minister Alfred Sauter on Sunday gave up all his posts in the CSU party, after he came under investigation over corruption claims related to masks procurement contracts.

Sauter has denied all claims.

A string of resignations

Meanwhile, CSU lawmaker Georg Nuesslein was last month placed under investigation for corruption following accusations that he accepted around €600,000 to lobby for a mask supplier.

A similar controversy embroiled CDU lawmaker Nikolas Loebel, whose company allegedly pocketed €250,000 in commissions for acting as an intermediary in mask contracts. 

On Thursday, Tobias Zech, a member of the Bundestag for the CSU Bavarian sister party of Merkel's CDU, became the latest in a string of MPs to resign over corruption allegations.

Zech had carried out paid PR work for a political party in Macedonia shortly after he was elected to the Bundestag in 2016, according to Der Spiegel weekly.

The graft claims have cost the conservatives dearly.

With the first allegations erupting in the run-up to two key regional elections in the states of Baden-Wuerttemberg and Rhineland-Palatinate this month, voters punished the conservatives and handed them their worst-ever results in both states.

The conservatives are now polling at just 29% nationally, their lowest level of support for a year and below the 32.9% they secured in the 2017 elections, according to a survey published by the ARD broadcaster on Thursday.