WASHINGTON (Reuters) -- US intelligence agencies are investigating whether chemical weapons were used this week in Syria, as both sides of the two-year conflict claim, but have not made a determination yet, a US intelligence official said Thursday.

"The intelligence community has not made an assessment at this point," the intelligence official told Reuters on condition of anonymity. "The information has not pushed us far enough in one direction for us to make an assessment yet."

Syrian President Bashar Assad's government and rebels accused each other of using chemical weapons in a rocket attack near Aleppo on Tuesday that killed 26 people.

President Barack Obama said in Israel on Wednesday that Assad would be held accountable if it were determined that chemical weapons had been used in Syria.

US Ambassador to the United Nations Susan Rice issued a statement on Thursday welcoming the announcement of a UN investigation.

"As the UN proceeds with these efforts, we will also continue to work closely with our partners to obtain further information regarding any and all credible allegations of the potential or actual use of chemical weapons in Syria," she said.

A Reuters photographer was told by some of those hospitalized after the attack on Tuesday of a strong smell of chlorine in the air and that many victims had fallen down dead after the blast.