During his closed-door meeting with Putin, the US president told his Russian counterpart that he expected meddling to stop in the 2018 election, according to the official.
Russian President Vladimir Putin danced arm-in-arm with Austria's Foreign Minister Karin Kneissl at her wedding on Saturday, after receiving an invitation that opposition critics said undermined the West's stance against Moscow.
The two leaders planned to make statements before the talks.
Nord Stream 2 was the subject of fierce criticism by US President Donald Trump at a July NATO summit, when he said the venture left Germany's government "totally controlled" by and "captive" to Russian Federation.
Russian Federation has shut off gas supplies to Ukraine in the past, with knock-on effects in the European Union.
Putin arrives in Germany after a stop at an Austrian vineyard to attend Foreign Minister Karin Kneissl's wedding to entrepreneur Wolfgang Meilinger.
The two leaders agreed in principle that Iran should exit Syria, according to the person, who discussed the matter on condition of anonymity.
Doctors find contact lens lost for 28 years in woman's eye
Experts believe this is extremely rare as our eyes are created to prevent such foreign objects from being unknowingly trapped. An MRI showed a "well-defined" cyst that measured eight by four by six millimeters just above her left eye.
Putin spokesman Dmitry Peskov told Russian news agencies that the Russian president spent about an hour at the wedding.
The United States and some European countries have criticized the pipeline, saying it could increase Europe's energy dependence on Russian Federation, harm Ukraine - now a major gas transit country - and pose an environmental risk.
"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 made clear that Ukraine should not be cut out: "Ukraine must, in my opinion, play a role in the transit of gas to Europe", even after the start of Nord Stream 2 in 2019. "Nord Stream 2 is exclusively an economic project".
With protesters audible Saturday outside the guesthouse in Meseberg, Putin also raised the issue of humanitarian aid and funding for worldwide reconstruction in Syria.
Opposition politicians have accused Kneissl of undermining European Union foreign policy by inviting Putin.
Russian Federation and the West remain locked in dispute over Moscow's annexation of Ukraine's Crimean Peninsula in 2014 and the conflict between Kyiv and Russia-backed separatists in eastern Ukraine.
On Syria, Germany wants Putin to finalize a lasting ceasefire there with the United States.