The Vatican has defrocked the anti-abortion US priest Frank Pavone for what it said were “blasphemous communications on social media” as well as “persistent disobedience” of his bishop.

A letter to US bishops from the Vatican ambassador to the US, Archbishop Christophe Pierre, said the decision against Pavone, who heads the anti-abortion group Priests for Life, had been taken and that there was no chance for an appeal.

Pavone had been investigated by his then diocese of Amarillo, Texas, for having placed an aborted foetus on an altar and posting a video of it on two social media sites in 2016. The video was accompanied by a post saying that Hillary Clinton and the Democratic party would allow abortion to continue, and that Donald Trump and the Republicans wanted to protect unborn children.

Pavone remains a firm supporter of Trump. His Twitter handle features him wearing a Maga hat with a background photo featuring the former US president, whom many conservatives praise for his supreme court nominees who overturned the landmark decision guaranteeing a constitutional right to abortion in the US.

Pavone was defiant in a tweet on Sunday, comparing his fate to that of unborn children. “So in every profession, including the priesthood, if you defend the unborn, you will be treated like them! The only difference is that when we are ‘aborted’ we continue to speak, loud and clear.”

His supporters immediately denounced the measure, including the bishop of Tyler, Texas, Joseph Strickland, who referred to Joe Biden’s support for abortion rights as “evil”.

Pavone had appealed to the Vatican over restrictions placed on his ministry in 2011 by the Amarillo bishop, succeeded in getting the restrictions eased and relocated away from Texas while remaining active with Priests for Life.

In his letter, Pierre cited information from the Congregation for Clergy that Pavone had been found guilty in a canonical proceeding “of blasphemous communications on social media and of persistent disobedience of the lawful instructions of his diocesan bishop”. The letter was first reported by Catholic News Agency.

The statement said Pavone was given “ample opportunity to defend himself” as well as to submit to his bishop.

The statement concluded that since Priests for Life is not a Catholic organisation, it would be up to the group to determine whether he could continue his role “as a layperson”.

Laicisation, or being reduced to the lay state, is one of the harshest sanctions in the church’s canon law.