Theological estrangement between East Syriac and West Syriac branches was manifested as a prolonged rivalry, that was particularly intensive between the Church of the East and the Maphrianate of the East (Syriac Orthodox Church). Both sides were claiming that their doctrines were not heretical, also accusing the other side of holding heretical teachings. Their theological estrangement continued to persist throughout medieval and early modern period, up to the present day. In 1999, the Coptic Orthodox Church, a sister-church of the Syriac Orthodox Church, blocked admittance of the Assyrian Church of the East to the Middle East Council of Churches, which has among its members the Chaldean Catholic Church, and demanded that it remove from its liturgy the mention of Diodorus of Tarsus, Theodore of Mopsuestia and Nestorius, whom it venerates as "the Greek doctors".