BERLIN — The China under-20 soccer team’s series of friendly games against fourth-tier clubs in Germany was postponed Friday because of the protests it could face.

The German soccer federation said in a statement that it had “substantial evidence of further escalation” against the team, which walked off the field during the first half of its game at fourth-division club TSV Schott Mainz last Saturday when a small group of spectators displayed Tibetan flags.

The China under-20 team had been due to face FSV Frankfurt for the second of its friendly games against teams from Germany’s southwest division this Saturday, but that match – and the following scheduled games against Hoffenheim’s second team and Wormatia Worms – were postponed at least until the winter break. The federation did not say when the games will take place.

“We sincerely regret having to postpone the series, especially considering what these games would have meant for the sporting development of the Chinese under-20 team and also the possible development of the southwest division,” German federation vice president Ronny Zimmermann said.

China’s under-20 team had been invited to play friendly games on free match-days made possible because of an uneven number of teams in the league. Sixteen of the league’s 19 teams were participating in the one-off action, which was supposed to help China’s under-20 team prepare for the 2020 Tokyo Olympics.

But the team’s players were incensed by the Tibetan flags on display in Mainz. They refused to continue playing for about 25 minutes until the flags were withdrawn. Players from the home side asked the protestors to remove the flags.

German federation president Reinhard Grindel defended the fans’ right to peaceful protest.

“It has been made clear to the Chinese federation that when you play in Germany you also have to deal with the fact that anyone can express their opinion,” Grindel said this week in response to criticism from Chinese foreign ministry spokesman Lu Kang.

Lu said the country firmly opposed any “separatist, anti-China or terrorist activities” defending Tibet and called for “mutual respect” from Germany as host toward its guest.

China has controlled Tibet for more than half a century. It sent troops to occupy the Himalayan territory following the 1949 communist revolution and contends that the region has been part of Chinese territory for centuries. Many Tibetans claim a long history of independence.

The German federation also faced criticism from within, with three teams – Waldhof Mannheim, Stuttgarter Kickers and TuS Koblenz – refusing to take part in the series of games despite a 15,000 euro ($17,700) bonus for each club.

Fan groups and team officials blasted the federation for the “excessive marketing of soccer” and for putting its own interests ahead of the clubs.

Christoph Radtke, the chairman of FK Pirmasens, which was one of six teams relegated from the four-tier league despite finishing 14th last season, accused the federation of “pure capitalism” for prioritizing the Chinese team over its own.

The German federation seemed surprised by the criticism.

“To the regret of all parties, the project did not get the expected broad approval,” the federation said Friday. “In fact, the project was used by a handful of spectators to send messages that were considered hurtful by the Chinese team and officials, the Chinese soccer federation’s support team and Chinese viewers.”

The federation said it will consult with its Chinese counterpart “to clarify in dialogue how to continue the project in the near future.”

“It is the firm intention of both associations to further strengthen the mutual connection,” the federation said.