Fred Phelps Sr, once pastor of the infamously intolerant Westboro Baptist Church, is close to death, according to his son.

Nathan Phelps, who has been estranged from his father for 30 years,posted a statement on Facebook which said: “I’ve learned that my father, Fred Phelps Sr, pastor of the ‘God Hates Fags’ Westboro Baptist Church, was ex-communicated from the ‘church’ back in August of 2013. He is now on the edge of death at Midland Hospice house in Topeka, Kansas.

“I’m not sure how I feel about this. Terribly ironic that his devotion to his god ends this way. Destroyed by the monster he made.

“I feel sad for all the hurt he’s caused so many. I feel sad for those who will lose the grandfather and father they loved. And I’m bitterly angry that my family is blocking the family members who left from seeing him, and saying their goodbyes.”

Nathan Phelps, the sixth of Fred Phelps Sr’s 13 children, ran away from home when he was 18. He now lives in Canada and works to promote LGBT rights.

The Topeka-based Westboro Baptist Church gained notoriety in the USand beyond through its practice of picketing funerals, often of service members killed in Afghanistan or Iraq but also of public figures, in order to promote a virulently anti-gay message under the slogan “God Hates Fags”.

The Calvinist group, usually only around 70-strong and which also propounds antisemitic and xenophobic views, has also picketed culturally sensitive sites such as Ground Zero in New York and attempted to disrupt the funeral of a child killed in a mass shooting in Arizona.

Other members of Phelps’s family and some followers have also left the church in recent years. No independent confirmation of Phelps’s reported excommunication was immediately available.

In 2011 the US supreme court ruled in favour of the church’s right to stage its protests, on grounds of free speech, after the father of a marine killed in Iraq in 2006 had won $5m (£3m) in damages for emotional distress caused by the pickets.

Writing the majority opinion in the case, Chief Justice John Roberts said: “Speech is powerful. It can stir people to action, move them to tears of both joy and sorrow, and – as it did here – inflict great pain. As a nation, we have chosen a different course – to protect even hurtful speech on public issues to ensure that we do not stifle public debate.”

In 2012 Barack Obama signed a controversial law making it more difficult for protesters to picket military funerals, prompting opposition from the American Civil Liberties Union.

The church was the subject of a famous documentary made by the British filmmaker Louis Theroux, entitled The Most Hated Family in America. In 2009 Fred Phelps Sr was denied entry to the UK.