David Cameron and Barack Obama - 'serious response' if chemical weapons in Syria
David Cameron and President Barack Obama have said that there'll be a "serious response" from Britain and America if it's discovered chemical weapons were used in the fighting there.
The two leaders spoke on the phone, and said there were "increasing signs" that the Syrian government had used the banned weapons in an attack earlier this week.
Hundreds of people are reported to have been killed in a suspected chemical weapons attack just outside the Syrian capital Damascus.
It's extremely difficult to work out what's happened in Syria as both sides of the conflict blame each other for attacks.
Rebel fighters claim that the Syrian government carried out the attack, but the government denies this, saying it was the rebels themselves.
If it's confirmed that chemical weapons have been used, it may mean other countries decide to get involved in Syria's war.
Chemical weapons, such as poison gases, are banned under international law because of the harm they can cause to people over a wide area.