The Chinese Football Association (CFA) announced on Sunday that it has canceled the national Under-20 team friendly series with German teams.

The cancelation came after Tibetan separatists waved flags interrupting a friendly match between China’s U20 team and a German fourth-tier Southwest Regional League team on November 18.

The following matches were suspended as China called for Germany to stop the separatist flag appearance while the German side said they cannot prevent it.

“In any circumstance the national core interest cannot be damaged, thus we decided to cancel the U20 team’s friendly program,” the governing body said in a late-night statement on Sunday.

“The CFA believes no football match should be interrupted by non-sport elements … Such things did not meet both sides’ principles nor FIFA regulations.”

China’s U20 team joined the friendly series along with 15 of 18 German fourth-tier Southwest Regional League teams.

The program was planned to run until May 2018, aimed at improving Chinese U20 team’s level as part of their preparations for the 2020 Tokyo Olympics.