British Prime Minister Theresa May (L) talks with President of the European Parliament Martin Schulz (R) ahead of a group photo at the Council of the European Union on the first day of a two day summit on October 20, 2016 in Brussels, Belgium | Jack Taylor/Getty Images Theresa May tells EU leaders not to hold summits without Britain UK leader says it will be ‘hard for me to accept things you agreed among yourselves.’

British Prime Minister Theresa May told other European leaders Thursday that they should not hold any more summits without the U.K., saying “otherwise it will be hard for me to accept things you agreed among yourselves,” according to a senior EU diplomat.

During her first EU summit in Brussels, May interrupted a discussion on migration to demand that there be no more such meetings that exclude the U.K., the diplomat said.

The other 27 EU leaders have held two informal meetings since the British referendum to leave the bloc: one a week after the vote and another last month in Bratislava. They plan to have another informal meeting without Britain in Malta in January.

“I accept that 27 needs to meet, but I want the U.K. to play an active part,” May said, according to the diplomat.

“Thus, we should meet as 28, otherwise it will be hard for me to accept things you agreed among yourselves. I expect to be fully involved in all discussions related to the EU 28.”

European Council President Donald Tusk, according to the source, responded that there were reasons for the 27 to meet without Britain and that she needed to accept that.

May thanked the leaders for "the welcome you have shown me," and specifically thanked Slovak Prime Minister Robert Fico, who is chairing the EU's rotating presidency, and Tusk for "briefing on Bratislava."

The leaders were expected to hear from May during a working dinner Thursday on the "current state of affairs" in Britain, but were not expected to hold a discussion specifically on Brexit.