The Organisation for Security and Co-operation in Europe expressed disappointment on Monday after Turkey's decision to bar two politicians who were part of a 100-strong mission to monitor the country's May 14 elections on Monday.
Danish MP Soren Sondergaard and Swedish MP Kadir Kasirga had their accreditations denied by Turkish authorities, the parliamentary assembly of the 57-member OSCE said.
"We are disappointed with this step taken by the Turkish authorities, which could impact negatively on the work of the international observer mission," the assembly said.
It said Turkey "should not, directly or indirectly, influence the composition of the mission".
It said Mr Sondergaard and Mr Kasirga had been refused entry because of statements made "as independent members of parliament".
The 100-strong team is made up of politicians from OSCE member countries.
Election rallies in Turkey ahead of May 14 elections - in pictures
Mr Sondergaard, from Denmark's Socialist-Green Alliance, said last week that Turkey had denied him access because he had previously visited the Kurdish-led Syrian Democratic Forces.
He told Danish public television TV2 that Ankara had accused him of "promoting a terrorist organisation".
The SDF led the fight against ISIS in Syria.
Turkey regards it as an offshoot of the Kurdistan Workers' Party (PKK), which it classifies as a terrorist organisation.
In 2018, Ankara barred two politicians, from Germany and Sweden, from an election observer mission sent by the OSCE's parliamentary assembly.
The OSCE was founded in 1975 to foster relations between the West and the Eastern Bloc. Its current members include Nato countries and Russia.