in Romania said that their MiG-21 fighter was shot down by a Ukrainian anti-aircraft missile
In Romania, they said that the MiG-21 aircraft of the national air force was shot down by an air defense anti-aircraft missile 
[Links nur für registrierte Nutzer].  Presumably, it was a missile of the S-300PS complex.
Earlier, Ukrainian media claimed that the Romanian Air Force MiG-21 Lancer fighter crashed.
 The plane disappeared from radar when it was over the Black Sea.  A  rescue helicopter was sent to search for him, which also crashed – this  was confirmed in the Romanian Air Force.
 As officially announced in Bucharest, the IAR 330 helicopter went in  the evening to search for the MiG-21 Lancer, with which radio contact  was lost.  The pilot managed to report bad weather and was ordered to  return to base, the Romanian Air Force said in a statement.  There were  five soldiers on board.
 By the way, according to media reports, the Romanian fighter escorted the Ukrainian Su-27.
 Recall that the President of Ukraine Volodymyr Zelensky blamed the  death of people in Ukraine on Western partners, who, according to him,  refuse to close the sky and provide aircraft.