Two prominent Syrian bishops who were kidnapped by armed rebels in the northern province of Aleppo, have been freed.

"The two are on their way to the patriarchy in Aleppo," Bishop Tony Yazigi of the Roman Orthodox Church said.

The men had warned of the threat to religious tolerance and diversity from the two-year conflict in their country,

SANA news agency said the Syriac Orthodox and Greek Orthodox Archbishops of Aleppo, Yohanna Ibrahim and Paul Yazigi, were seized by "a terrorist group" in the village of Kfar Dael.

It happened as they were "carrying out humanitarian work".

A Syrian member of the opposition Syrian National Coalition said the men had been kidnapped on the road to Aleppo from the rebel-held Bab al Hawa crossing with Turkey.

Several prominent Muslim clerics have been killed in Syria's uprising against President Bashar al-Assad.

The bishops are the most senior church leaders caught up in the conflict which has killed more than 70,000 people across Syria.

Christians make up less than 10% of the country's 23m people.

Many religious minorities have been wary of the mainly Sunni Muslim uprising against Mr Assad, whose Alawite sect is an offshoot of Shia Islam.

Religious groups fear for their future if rebels were to end 40 years of Assad dynastic rule, which ensured religious freedom without political rights.

Fears have increased with the growing strength of Islamist rebels and a pledge of allegiance to al-Qaeda by the hardline al-Nusra Front rebels two weeks ago.

The two men were driving to Aleppo when they were kidnapped.

Last September hundreds of Christian families fled Aleppo as rebels and soldiers battled for control of the country's biggest city.

Neighbouring Iraq, where sectarian violence after the 2003 overthrow of Saddam Hussein forced half the Christians to flee, offers frightening parallels for Syrian Christians.

The revival of Islamists in the 2011 Arab uprisings in Tunisia, Libya and Egypt also fills Syria's Christians with foreboding.

Writing in January, Bishop Yazigi said it was important that the uprisings known as the "Arab Spring" should not jeopardise centuries of religious diversity in the Middle East.

"What is the spring without the diversity and richness of colours in comparison with the haze...of winter? Diversity is richness while monochromatic uniformity is a ticking bomb that kills its owner," he said.