Last Updated May 25, 2017 6:19 PM EDT
In video of the incident, a group of leaders is seen walking together and talking, and as the group comes to a stop, Mr. Trump grasps Markovic's right arm and pushes past him to get to the front of the group. Markovic appears surprised but smiles and pats the president on the back. The president does not acknowledge him.
Mr. Trump then straightens his jacket and has a brief conversation with Lithuanian President Dalia Grybauskaite.
Markovic is brushing off the incident, according to the Associated Press, and he said that it was only "natural" that Mr. Trump be in the front row.
"I didn't really register it, I just saw reaction to it on social networks," he said. "It is quite simply a harmless situation. I don't take it any other way. So today I really had a unique opportunity to personally thank President Trump for his support, quick ratification of protocol at the US Senate and for the overall support of the United States of America in Montenegro's integration into NATO and of course for a further development of our bilateral relationships. But since today journalists are referring to that scene in different ways I would also wish to tell you that it is natural that the president of the United States is in the front row."
This is not the first awkward exchange President Trump has had on his visit to NATO. Earlier in the day, the handshake with newly-elected French president Emmanuel Macron was described by the pool reporter as having been "so long that knuckles started to turn white." NATO leaders also stood by during the dedication of a 9/11 memorial, when the president told them their contributions are too low. Mr. Trump also had to reckon , who is upset over the leak to the U.S. media of British intelligence on the Manchester attack.
Neither Montenegro nor its prime minister are particularly well-known in America, but on June 5, the country is expected to become the 29th member of NATO, completing a process that began in 2003 when Montenegro was still part of a union with Serbia and restarted in 2006 after gaining independence.
The president's shove is a minor indignity, compared with what Markovic has had to withstand from Russia. In an interview with Time Magazine, Markovic talked about his country's own ongoing investigation of Russian interference in its elections—a failed Russian plot to stage a coup d'état to seize power, assassinate the former prime minister, and install a leader that would keep Montenegro out of NATO.
Still, Markovic, in the interview, insisted that the two countries still maintain a friendship, and that the reason for joining NATO is to end the historic cycle of conflict in the Balkans, not to oppose Russia.
"Montenegro has cherished for more than 300 years its good friendship with Russia, and we would never allow our country to be misused in order to disrupt Russian security in any way," Markovic told Time magazine.
"Nevertheless, we are going to defend our own interests and the interests of this Western community that we opted for."
Montenegro will be the last of the countries with an Adriatic coastline to join NATO and is also in talks to become a member state of the European Union.