Syria has condemned Israel after air strikes against Damascus, saying the attacks aim "to give direct military support to terrorist groups".
President Barack Obama said he does not foresee a scenario in which he would send US ground troops to Syria.
Israel claim that Syrian government forces have used a chemical weapons likely to be the nerve gas Sarin in their fight against rebels.
President Barack Obama has said the US expects to find more evidence of the use of chemical weapons in Syria, but warned that rushing into the conflict could cause problems on the ground.
Obama added that the US is already engaged, on a day-to day basis, in trying to deal with the crisis
He said the US is investigating to "get a better handle on the facts inside of Syria".
Speaking at in press conference in Costa Rica, Obama added: "If there is the kind of systematic use of chemical weapons inside of Syria - we expect that we are going get additional, further evidence - at that point we will present that to the international community".
He went on to warn: "When we rush into things, when we leap before we look, then not only do we pay a price, but often times we see unintended consequences on the ground. It's important for us to do it right."
The US believes Israel has conducted an air strike into Syria, CNN has reported, quoting unnamed US officials.
The news network claimed US and Western intelligence agencies are reviewing classified data showing Israel is most likely to have conducted a strike between Thursday Friday, according to two US officials.
CNN report this was the same time frame that the US collected additional data showing Israel was flying a high number of war planes over Lebanon.
The Israel Defence Force tweeted:
Breaking: Direct hit confirmed on Global Jihad-affiliated terrorist in Gaza Strip. Hit was in response to rocket he fired at Israel. 1/2From @IDFSpokesperson on Twitter:
A 29-year-old police officer was killed in an Israeli air strike in the Gaza Strip, according to Ashraf al-Kidra, Gaza's health ministry spokesman.
However there was a conflicting report from Israel's Channel 2 TV claiming the air strike targeted an Islamic militant involved in a recent rocket attack on the southern Israeli town of Eilat.
The Israeli military confirmed that it carried out an air strike on Gaza but gave no further details.
A Palestinian has been killed in a blast which Hamas blamed on an Israeli air strike, a Gaza hospital told Reuters.
A motorbike has been targeted in a strike by an Israeli aircraft near a Hamas training camp in Gaza, Hamas Radio reported.
Sarin is a human-made chemical warfare agent classified as a nerve agent and is the most toxic and rapidly acting of the known chemical warfare agents. It is similar to certain kinds of pesticides, called organophosphates, but is much more potent.
- Sarin originally was developed in 1938 in Germany as a pesticide.
- Sarin is a clear, colourless, and tasteless liquid that has no odour in its pure form. However, sarin can evaporate into a vapour (gas) and spread into the environment.
Symptoms appear within a few seconds after exposure to the vapour form of sarin and within a few minutes and up to 18 hours after exposure to the liquid form.
Symptoms of exposure include:
- Runny nose and watery eyes
- Small, pinpoint pupils, blurry vision and eye pain
- Drooling and excessive sweating
- Coughing, tightness in the chest and rapid breathing
- Confusion, weakness and drowsiness
- Altered heart rate or blood pressure
Sarin is the most volatile of the nerve agents, which means that it can easily and quickly evaporate from a liquid into a vapour and spread.