U.S. President Barack Obama said here Wednesday that it is too early for him to make any judgement on the reported use of chemical weapons in Syria before a thorough investigation into the incident.

"With respect to chemical weapons, we intend to investigate thoroughly exactly what happened," Obama told reporters after holding a closed-door meeting with Israeli Prime Minister Benjamin Netanyahu.

"Obviously in Syria right now, you've got a war zone, you have information that's filtered out, but we have to make sure that we know exactly what happened, what was the nature of the incident, what can we documented, what can be proved," said Obama, who arrived here Wednesday on his first visit to Israel as U.S. president.

"So I've instructed my teams to work closely with all other countries in the region and international organizations and institutions to find out precisely whether or not this red line was crossed," he added.

At the United Nations, Syria has asked UN chief Ban Ki-moon to appoint an independent mission to investigate an alleged chemical weapon attack which the Syrian government has blamed on rebels in northern Syria. The rebels have denied the government's claim and blamed government forces for Tuesday's missile attack on Khan al- Assal village in northern Aleppo province.