"It is certainly a geopolitical project aimed to weaken Ukraine". Merkel has said a certain level of gas transit through Ukraine must be ensured.
Prior to the meeting, Merkel said she would discuss the conflicts in Ukraine and Syria, as well as Iran and the Nord Stream 2 gas pipeline project with Putin.
The independent foreign minister first met the Russian president 17 years ago at a summit in Slovenia with the then US President George Bush in July 2001.
"Nord Stream 2 is exclusively an economic project".
Russian Federation and the West remain locked in dispute over Moscow's annexation of Ukraine's Crimea Peninsula in 2014 and the conflict between Kyiv and Russia-backed separatists in eastern Ukraine.
Putin's meeting with Merkel late Saturday takes place at the German government's guesthouse in Meseberg, north of Berlin.
"We want to create new momentum in the Minsk (peace) process", German Foreign Minister Heiko Maas said in an interview to be published by Die Welt am Sonntag on Sunday. Merkel also supports the deal, but noted that Germany is "following Iran's activities with concern, be it the missile program or the situation in Syria".
Putin told reporters that everything must be done to help Syrian refugees to return to their country and that Syria needed assistance to rebuild. "These are the most basic things in which I think everyone is interested, including Europe". Kneissl is an appointee of the far-right Freedom Party, which has long-standing ties with Russian Federation.
Ukranian officials are concerned Russia could stop delivering natural gas through Ukraine, which works as a transit country for Russian natural-gas export to the European Union and levies a fee on the trade, after Gazprom's transit contract expires at the end of 2019, since there would be less demand for it.
"It is completely unacceptable for Kneissl to invite Putin privately to a party", he told Austrian newspaper Der Standard.
Michel Reimon, an Austrian Green member of the European parliament (MEP) called on Kneissl to resign from her post.
Yet the foreign ministry insisted that Putin's visit "will not change anything in terms of Austria's foreign policy positions".
Putin spent around an hour at the wedding and gave the newlyweds a cold press oil machine and a landscape painting depicting "where the groom hails from" as a present, according to Kremlin spokesman Dmitry Peskov.