US president Barack Obama has issued a stern warning to the Syrian regime, which has reportedly threatened to use chemical weapons to deter foreign intervention.

"They will be held accountable by the international community and the US, should they make the tragic mistake of using those weapons," Obama said.

"They should not think one iota about using chemical weapons," said George Little, Pentagon press secretary.

The US State Department maintained that any possible use of chemical weapons would be completely unacceptable.

Israel also voiced its concern over the stockpile of Syria's chemical weapons, saying the arsenal will pose a "great threat" if it falls into the hands of Islamist groups such as Lebanon's Hezbollah.

"Could you imagine Hezbollah, the people who are conducting with Iran all these terror attacks around the world - could you imagine them having chemical weapons? It would be like al-Qaida having chemical weapons," Israel's prime minister Benjamin Netanyahu told Fox News.

UN Secretary General Ban Ki-moon expressed concern over the prospect of the Assad government using chemical armaments against its own people, adding: "It would be reprehensible if anybody in Syria is contemplating the use of such weapons of mass destruction."

"All these types of weapons are in storage"

A top-ranking official in Damascus said on 23 July that President Assad's government will not use chemical and biological weapons against its own citizens. However, it will not hesitate to use them in cases of "external aggression".

"All of these types of weapons are in storage [securely] and under the direct supervision of the Syrian armed forces and will never be used unless Syria is exposed to external aggression," the foreign ministry's Jihad Makdissi said on Syrian state TV. Makdissi's statement is the first time the Syrian regime has publicly hinted at the use of chemical or biological weapons.

It is believed that Syria's chemical weapons programme has been active since the 1980s, and the country possesses the fourth-biggest stockpile of such armaments in the world.

Given that Syria is not a party to the international Organisation for the Prohibition of Chemical Weapons (OPCW), this arsenal has become a major source of concern for the US and other world leaders.

Meanwhile, fierce fighting is continuing in Aleppo, the largest city in Syria, with contrasting reports detailing key gains for both sides.

While some reports claim that the rebels have taken the neighbourhood of Salah el-Din, others says that government forces have recaptured several neighbourhoods, and are now combing the areas for rebel fighters.

Large numbers of Syrians are fleeing the country every day. According to estimates of the humanitarian organisation Syrian Arab Red Crescent, nearly 115,000 Syrians have fled the country. since the conflict began. It also says that nearly 1.5 million Syrians have been made homeless since the battle against President Bashar al-Assad began 16 months ago.