Russian President Vladimir Putin has started the second day of his visit to Buenos Aires, where a G20 summit is taking place, with a working breakfast with German Chancellor Angela Merkel, TASS reported.
Merkel was on her way from Germany to the summit when the government's Airbus A340 made an unscheduled but safe landing at Cologne-Bonn airport late on Thursday.
"It was a serious malfunction", Merkel told reporters hours later, after the delegation was brought to a hotel in Bonn.
Merkel was due to hold bilateral meetings with Russian President Vladimir Putin and United States leader Donald Trump on the sidelines of the summit on Friday, but her delayed arrival has thrown her schedule into disarray.
Video from on board shows several fire engines surrounding the Airbus after it landed.
Merkel's plane, named after Konrad Adenauer, had to return after just an hour into the 15-hour flight to Buenos Aires after experiencing "technical malfunction".
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"Luckily, we had an excellent crew and the most experienced pilot of the special air mission wing", Merkel said.
The German military blog Augengeradeaus reported that the plane's transponder was transmitting the code 7600 which refers to a radio malfunction.
Merkel will now travel to the G20 with a vastly slimmed-down delegation.
Merkel has had to reschedule some meetings due to the delay. She is due to arrive in time for the summit leaders' dinner on Friday.
The German air force on Friday ruled out sabotage, with a spokesman telling national news agency DPA that "there is absolutely no indication of a criminal act".