Speculation over the use of chemical weapons in the Syrian conflict is rising. On April 25, United States officials said its intelligence community believes President Bashar al-Assad's forces are likely to have used chemical weapons, specifically chemical agent sarin, on a small scale against the rebel fighters.

Since the US has said it would not tolerate the use of chemical weapons by Assad in the conflict (meaning that by doing so Assad would invite direct US action against himself), the unverified intelligence could have grave consequences on the Syrian conflict.

The Syrian government has denied the West's allegations that it has used chemical weapons and, instead, has claimed that such weapons had been used by the opposition forces. Syrian Information Minister Omran al-Zoubi said the chemical weapons used by the rebels in a northern Syrian town of Khan al-Assal in Aleppo province were probably acquired from Turkey because the missile, which targeted the town, was fired from a rebel-held base not far from the Turkish borders.

So far there is "no conclusive proof" that either side in the Syrian conflict has used chemical weapons. The US intelligence community's assessment of the possible use of chemical weapons in Syria are preliminary and disputable. Given the stakes involved and the consequences of using unverified intelligence to invade Iraq more than a decade ago, the Barack Obama administration has been careful in its commitment, saying that the US needed definitive proof before taking action.

During the more than two-year-old conflict, the opposition may have made considerable achievements but it is still not capable of toppling the Assad government without direct foreign military intervention. The US has repeatedly said that the use of chemical weapons would be a game changer and it would take appropriate action against it.

But if the Syrian government crosses the "red line" set by the US (that is, uses chemical weapons), the real beneficiary would be the opposition. So the possibility of the opposition leveling false charges against the Syrian government when it comes to the use of chemical weapons cannot be ruled out. Assad is full aware that the use of chemical weapons, that is, if he has any, is not helpful to his government, for it would invite Western military intervention in Syria. And after Obama set a "red line" for the Syrian government, Assad dare not cross it given the immense pressure he is in. So the West's claim that Assad is likely to have used chemical weapons is not convincing at all.

Since the outbreak of the conflict in Syria, the West has been worried about the possibility of the Assad government having chemical weapons. Syria reportedly makes Sarin, Tabun, VX and mustard gas-type chemical weapons. On July 23, 2012, Syria claimed that it had some chemical weapons, reserved for national defense against foreign countries, but the government would never use these weapons against Syrian citizens.

In other words, that Syria has chemical weapons is not a secret and the key issue is whether the Syrian government has used them. Syria is not a party to the Chemical Weapons Convention, and chemical weapons have become the Assad government's trump card but their use can prompt external forces to join the conflict.

Chemical weapons, a highly serious and sensitive issue, has a direct bearing on the developments of the Syrian crisis, the country's future, regional stability and international security. Assad has been treading with extreme caution on the issue and will not dare to cross the line. But the Syrian government cannot avoid the issue of chemical weapons even after repeatedly denying that it has ever used them.

A UN team was ready to investigate the alleged use of chemical weapons in Syria when, fearing a repeat of Washington's actions before the invasion of Iraq in 2003, Syria said it cannot trust UN investigators (from the US and Britain) and instead wanted Russian experts to investigate the issue.

Many Western experts and leaders might try to convince Obama that Assad has crossed the "red line" and hence this is the time to act. But without concrete proof that the Syrian government has used chemical weapons, the US is unlikely to intervene militarily in the Syrian conflict. Nevertheless, other countries may use the chemical weapons issue to intervene in the Syrian conflict. The situation in Syria remains fluid and the international community is monitoring it closely.

The author is a researcher at the Institute of West Asian and African Studies, affiliated to the Chinese Academy of Social Sciences.