Police in Manchester are investigating claims that an imam at a British mosque attended by the arena bomber delivered a sermon advocating armed jihad six months before the attack.

Greater Manchester police (GMP) said they had been passed footage from the BBC purporting to show an imam at Didsbury mosque praising mujahideen fighting abroad – a term commonly used for Islamist guerrilla fighters.

Mustafa Graf was recorded in the south Manchester mosque in December 2016 praying for “victory” for “our brothers and sisters right now in Aleppo and Syria and Iraq”, the BBC reported. The imam also seemed to suggest that those who stayed in the UK did nothing to support their Muslim comrades in the Middle East.

Graf insists his words were misinterpreted by Islamic scholars who worked with the BBC on the Arabic translation and said that it referred to “military jihad”. He denied he had called for armed jihad or preached extremism.

The trustees of Didsbury mosque said Graf’s sermon was highlighting the plight of Syrians and his use of the words “jihad” and “mujahideen” had been misinterpreted.

“We do not tolerate or instigate any form of preaching that breaches both Islamic principles and the laws of England and Wales,” the mosque said in a statement.

In the sermon, Graf allegedly said: “Lots of brothers stayed behind, unfortunately. They love Islam and Muslims but they do nothing for the support of their brothers and sisters.”

Another passage of the sermon purportedly said: “Jihad for the sake of Allah is the source of pride and dignity for this nation.”

After the bombing by Salman Abedi on 22 May last year, the Guardian learned that his father had worked at the mosque before leaving for Tripoli. One of the imams, Mohammed Saeed, described how Salman Abedi attended regularly and had once looked at him “with hate” when he gave a sermon criticising Islamic State in Libya.

Saeed said he gave a strong sermon against terrorism and about the sanctity of life in 2015. He said 2,000 members of the mosque were with him; a small number were not, including Abedi.

Ten days after Graf’s December 2016 sermon, Abedi bought a ticket for the Ariana Grande concert, the BBC said. Six months later he detonated a suicide bomb, killing himself and 22 others, and injuring many more. It is not clear if Abedi ever heard the sermon, but the BBC said he had connections with a group led by Graf.

The broadcaster said it had obtained footage of Abedi attending a demonstration in London against a secular Libyan general who was fighting against Islamist militia. The event was organised by the 17th of February Forum protest group, led by Graf.

A GMP spokesperson said: “We have been handed the material from the BBC following their broadcast and will now review it to establish if any criminal offences have been committed.”