"I cannot hide that I am concerned about this development in Russia and (these) domestic discussions about discrimination of sexual minorities in Russia," German Foreign Minister Guido Westerwelle told reporters while on a visit to Lithuania.
"We think any kind of discrimination of sexual minorities, gays or lesbian for example, (is) not acceptable," the openly gay minister said in the central city of Kaunas.
Westerwelle spoke soon after Russian lawmakers passed a bill Friday that bans people in countries where same-sex marriage is legal from adopting Russian orphans.
The bill's wording implies that couples in a heterosexual marriage would still be allowed to adopt Russian children. But single people would be banned, regardless of their sexual orientation.
It must still be passed in the upper chamber, which will convene on Wednesday, and be signed by President Vladimir Putin to become law, but the Russian leader has already backed the bill and vowed to sign it.
The restriction would follow the approval last year of an adoption ban for citizens of the United States despite massive protests and petitions by thousands of people against the legislation.
Same-sex marriages are currently legal in 14 countries, including Canada, Belgium, Spain, Norway and Sweden. France became the latest addition to the list in May, after months of huge division over the issue.
Germany allows registered partnerships - a status that falls short of marriage under the law - but gay couples are still forbidden from adopting children there.