Contracts for Berlin-based Stark Defence, where Thiel holds a stake, and Munich-based Helsing to supply the attack drones will come before parliament's budget committee next week.

Greens MP Sara Nanni, a security policy spokeswoman for her party, told AFP on Thursday that the controversial right-wing billionaire's influence raises possible problems.

The strategic importance of the deal means that investor-related risks need to be carefully vetted, she said, adding that "I have to take a very close look at it".

The German-born Thiel, a co-founder of tech firms PayPal and Palantir and a key early investor in Facebook, is a close confidante of US President Donald Trump.

His right-wing libertarian views and outspoken scepticism of liberal democracies have made him a highly polarising figure.

Dietmar Bartsch of the far-left Die Linke called for halting the deal, arguing to AFP that paying billions to a firm sponsored by "an avowed opponent of liberal democracies is unacceptable".

Defence Minister Boris Pistorius, a Social Democrat (SPD), also expressed reservations when he said Tuesday that, before awarding the contract to Stark Defence, it must be clarified "what influence Mr Thiel actually has".

The proposed contracts have an initial combined value of 536 million euros ($630 million) but include options that could expand the value into the billions.

The chairman of parliament's defence committee, conservative MP Thomas Roewekamp, largely dismissed concerns about Thiel in comments to the RND news network.

The "small stake held by an American investor" is only of "minor importance", he said, adding that the drones are urgently needed, particularly to defend German troops deployed to NATO's eastern flank in Lithuania.

Roewekamp said there remained "open questions regarding the price, the quantity and the technical capabilities" of the drones -- but that those issues can be resolved "through the usual parliamentary process".

Stark Defence declined to disclose details about Thiel's stake, other than that is remains below 10 percent.

Thiel's stake does not involve outsized special rights or influence, the company said, and outside access to confidential technical information is regulated by German authorities.

Speaking generally, lawmakers such as Nanni have voiced support for taking risks in order to build up Europe's tech and defence industries.

"If we don't want to buy high-tech equipment from the US, then we also have to be prepared to take on more risk," Nanni told AFP.

SPD MP Andreas Schwarz, a budget and defence policy expert, told AFP there is still broad support in parliament for awarding the drone contracts.

He also noted that Thiel "has stakes in other software companies used by German authorities and NATO".

But if the defence minister thinks more clarity is need about Thiel's influence, then "parliament will support him in this," Schwarz said.

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