Al-Qaeda leader Ayman al-Zawahri has criticised US treatment of hunger striking inmates at Guantanamo Bay and said the group would spare no effort to free them.

The comments were made in an audio recording posted online this morning.

Mr Zawahri also said Hezbollah's intervention in the conflict in Syria was an attempt to promote Iranian hegemony over the country.

"The [hunger] strike by our brothers at Guantanamo unmasks the true ugly face of [the United States of] America," Mr Zawahri said in the recording posted on an Islamist website.

The authenticity of the recording could not be verified.

"We pledge to god that we will spare no effort to free all our prisoners," he said.

He did not elaborate on what al-Qaeda intended to do.

The group has claimed responsibility for simultaneous raids on two Iraqi prisons last week in which they said more than 500 inmates had been set free.

And in Pakistan, the Taliban broke 250 prisoners out of a jail yesterday.

166 men, most of whom were rounded up in counter-terrorism operations since the 11 September 2001 attacks on the United States, are currently being held at a US military base in Guantanamo Bay in Cuba.

Many have been on hunger strike to protest their indefinite detention, with some being force-fed.

Mr Zawahri also denounced the US use of drone strikes targeting Islamists, saying it was a sign of the defeat of US campaigns in Afghanistan, Pakistan and Yemen.

Drone strikes have been widely criticised by rights groups who say the strikes often miss their targets and hit civilians.

"These spying planes will not protect you from defeat, but rather are a sign of your failure and the repeated failure of your government," Mr Zawahri said, addressing US President Barack Obama.

"You are leaving a legacy of hatred and demands for vengeance from you over your crimes," he added.

Mr Zawahri, whose Sunni Muslim network adheres to an austere view of Islam that views Shia Muslims as infidels, also condemned the involvement of Lebanese group Hezbollah in Syria's civil war, singling out its leader Sayyed Hassan Nasrallah.

"It has become clear to the Muslim nation that he is but a tool in the Safavid, rejectionist project which seeks to impose the authority of Shi'ite jurisprudence ... on the nation of Islam through slaughter, repression, torture and by supporting one of the most corrupt, tyrannical and criminal regimes," the al-Qaeda leader said.