The leader of Al-Qaeda delivered a sinister message to young Muslim men in the United States and other Western countries, encouraging them to carry out attacks in their home countries.

Terror leader Ayman al-Zawahiri makes the call to arms in an audio recording that was posted online on Sunday.

He also urges militant groups across the world to establish a greater unity in their jihads.

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Homegrown attacks: Terror leader Ayman al-Zawahiri (pictured in 2013) makes the call to arms in an audio recording that was posted online on Sunday

‘I call on all Muslims who can harm the countries of the crusader coalition not to hesitate,’ he said in the recording, referring to the nations making up the Western-led coalition in Iraq and Syria.

'We must now focus on moving the war to the heart of the homes and cities of the crusader West and specifically America.'

We must now focus on moving the war to the heart of the homes and cities of the crusader West. Al-Qaeda leader Ayman al-Zawahiri

The leader suggests Muslim youths take their inspiration from Tsarnaev and the Kouachi brothers, who carried out the Boston marathon bombings and the Charlie Hebdo shootings in Paris respectively.

It was not clear when the audio recording was made, but references to former Taliban leader Mullah Mohamed Omar as being alive suggest it is at least two months old.

Omar’s death was announced by the Afghanistan government in late July.

Zawahiri reiterated his position on Islamic State, repeating what he said in a recording posted on Wednesday – that he viewed the group’s claim to be a caliphate as illegitimate but would join them in fighting Western and secular forces in Iraq and Syria.

Terror leaders: Ayman al-Zawahiri (right) sits with his predecessor Osama bin Laden (left), to whom he acted as adviser, in March 2004

Zawahiri urged unity between Islamist factions in Syria and Iraq, where a Western-led coalition is bombing Islamic State targets, but recognised it would be difficult.

Despite the big mistakes [of Islamic State], if I were in Iraq or Syria I would cooperate with them in killing the crusaders and secularists and Shi’ites. Al-Qaeda leader Ayman al-Zawahiri

The former doctor called for the formation of an independent sharia court to settle disputes.

Al-Qaeda have found themselves struggling to keep up with ISIS’ powerful social media presence, and lagging behind in the militant propaganda war.

The audio-recording appears to be an attempt to garner more support for their cause, and remind the world that there is more than one militant terror group.

Despite dismissing ISIS and its leader Abu Bakr al-Baghdadi as illegitimate, Zawahiri hinted this week at cooperation in their fight against the West.

The Egyptian, who replaced Osama Bin Laden, accused the militants of sedition and insisted their most senior figure does not deserve to be ‘caliph’, or ruler.

He insisted that Al-Qaeda does not recognise the caliphate.

Teaming up?: Despite dismissing ISIS and its leader Abu Bakr al-Baghdadi as illegitimate, Zawahiri hinted this week at cooperation in their fight against the West. Pictured, ISIS fighters holding the al-Qaeda flag with 'Islamic State of Iraq and the Levant' written on it, in October 2013

Zawahiri, who has a $25million U.S. bounty on his head, added that he was surprised that Baghdadi appointed himself as the leader without consulting the rest of the Muslim world.

ISIS has declared a caliphate in large parts of Iraq and Syria under its control and sought to expand its power in the Middle East, becoming a greater security threat than al-Qaeda in the strategic oil-producing region.