The trustee of a mosque linked to the family of the Manchester suicide bomber has denied it is a breeding ground for extremism, as it was revealed that he was behind offensive tweets about Jews.

Farzi Haffar from Didsbury mosque this week sought to calm fears about radicalisation, despite having sent social media messages commenting on “the Jewish lobby” and describing Israelis as Nazis.

Haffar, who denied that concert bomber Salman Abedi had visited the mosque, did say the killer’s father, Ramadan, had used it.

“We’ve never seen him,” said Haffar, referring to the 22-year old suicide bomber, who killed 22 people and injured more than 110 people on Monday. “His father who used to pray here is in Libya. Lots of Libyans prayed here.”

Asked about extremism, Haffar added: “We have never had a concern here about radicalisation. I am part of a police advisory group. We do not want to end up with radicals and we are very careful about the imams we employ. We have never had concerns and we have been horrified since yesterday.”

However, Jewish grassroots groups were quick to point out that Haffar had previously sent a number of inflammatory tweets, including one reading: “The more these radical and fundamental #Jewish invaders attack #Moslem and #Christian #Arab holy areas in Palestine, the more hate there is.”

In another, he retweeted someone writing about “joy/applause for breaking taboo, comparing Israelis to Nazis”.

Colonel Richard Kemp, a former British Army commander, said Haffar’s tweets were “incitement to hatred”.