President Donald Trump meets with Japanese Prime Minister Shinzo Abe during a meeting on the sidelines of the G-20 summit in Osaka, Japan, Friday, June 28, 2019. (AP Photo/Susan Walsh)
President Donald Trump meets with Japanese Prime Minister Shinzo Abe during a meeting on the sidelines of the G-20 summit in Osaka, Japan, June 28, 2019.

U.S. President Donald Trump is set to begin a series of one-on-one meetings with at least eight world leaders on the sidelines of the Group of 20 summit in Japan. 

His first meeting Friday was with summit host Prime Minister Shinzo Abe of Japan, followed by Indian Prime Minister Narendra Modi and German Chancellor Angela Merkel — all of whom Trump criticized  just hours before he landed in Osaka.

"We'll be discussing trade, we'll be discussing military,'' Trump said as he met with Abe before heading to the talks. 

Trump, recently, had publicly criticized the U.S.-Japan defense alliance, that has been in place since World War Two.

"If Japan is attacked, we will fight World War Three. We will go in and protect them with our lives and with our treasure," Trump said during a telephone interview with Fox Business News on Wednesday. "We will fight at all costs … but if we are attacked, Japan doesn't have to help us at all. They can watch on a Sony television."

U.S. Secretary of State Mike Pompeo, left, talks with Indian Prime Minister Narendra Modi during their meeting at the Prime Minister's Residence, June 26, 2019, in New Delhi, India.

Trump met jointly with Abe and Modi. The three leaders did a joint fist bump for the reporters. Despite earlier complaining about India, Trump said he and Modi have become "great friends'' and the two countries "have never been closer.'' 

As for Germany, Trump complained again that Berlin was not contributing enough toward the costs of the North Atlantic Treaty Organization.

The most attention Friday, however, will likely be paid to the meeting between Trump and Russian President Vladimir Putin. 

As he left the White House Thursday, Trump told reporters that he expected a "very good conversation'' with Putin but added that "what I say to him is none of your business.'' 

The two leaders are expected to discuss how to contain Iran, which has threatened to very soon breach uranium enrichment limits set in the 2015 nuclear accord. They will also most likely take on the subjects of Syria and Venezuela. 

Russian President Vladimir Putin speaks during an annual nationwide televised phone-in show in Moscow, June 20, 2019.

It will be the first meeting between the two leaders since special counsel Robert Mueller's investigation failed to find evidence that the Trump campaign had criminally conspired with Russia during the U.S. presidential election in 2016.

Last November, Trump canceled a meeting with Putin at a G-20 summit in Argentina after Russia seized two Ukrainian vessels and their crew in the Sea of Azov, but the continued detention of those crew members does not appear to be deterring the leaders from meeting this time. 

On Saturday, Trump is scheduled to meet with China's Xi Jinping when they are are likely to discuss trade after a breakdown in negotiations and an escalation of tariffs by both sides.

After the summit, Trump will fly to Seoul to discuss with South Korean President Moon Jae-in ways to ease tensions with North Korea. It is speculated that the U.S. president will visit the Demilitarized Zone separating the Koreas, but U.S. officials have ruled out a meeting between Trump and North Korean leader Kim Jong Un while the U.S. president is on the peninsula.