The head of the Catholic Church in Ethiopia was barred from leaving the main airport in neighbouring Eritrea to attend an engagement over the weekend.
The church said Cardinal Berhaneyesus Demerew had been issued with a visa, which Ethiopians now get on arrival following a 2018 peace deal.
But airport officials said their orders had come from "higher up".
The government has been unhappy with the Catholic Church since bishops called for political reform last year.
In response, the authorities closed down Catholic-run schools and hospitals, saying it was imposing old regulations that stipulate that religious bodies cannot run such institutions.
The country, led by President Isaias Afwerki, does not have a functioning constitution and has never held a national election.
His Ethiopian counterpart, Prime Minister Abiy Ahmed, was awarded the 2019 Nobel Peace Prize for ending a 20-year military stalemate with Eritrea following a 1998-2000 border war.
How influential is Cardinal Berhaneyesus?
The cleric is a highly respected figure in Ethiopia, where most Christians are members of the Orthodox Church, and was appointed by Mr Abiy to head the national reconciliation commission.
He had been due to attend an event marking the 50th anniversary of the construction of Kidane Mehret Cathedral in Eritrea's capital, Asmara.
He had arrived at Asmara airport on Saturday, but was obliged to return to Ethiopia the next afternoon after fruitless attempts to reach the crowd gathered to welcome him.
The Eritrean government has not commented on the issue.
Roman Catholics make up about 4% of Eritrea's population.
The church is one of only four religious groups allowed to operate in Eritrea, along with the Eritrean Orthodox, Evangelical Lutheran and Sunni Islam groups.
The government regards other religious groups as instruments of foreign governments.