UNITED NATIONS -- A team of UN chemical weapons inspectors in Syria carried out their first day of investigation despite a sniper attack against their convoy, UN Secretary-general Ban Ki-moon said on Monday.

"I just spoke to my Under-Secretary-General for Disarmament, Ms. Angela Kane, who is now in Damascus to oversee the investigation. The first day of investigation was carried out by Dr. Sellstrom and his team," said Ban in a statement issued here by his spokesperson.

"What I am told at this time is that their vehicle was attacked by an unknown sniper, but despite such very difficult circumstances, our team returned to Damascus and replaced their car and proceeded to a suburb of Damascus to carry on their investigation," said the secretary-general.

According to the statement, during their first day of investigation, the UN experts "visited two hospitals," " interviewed witnesses, survivors and doctors" and also "collected some samples" at the site of the latest alleged use of chemical weapons on Aug. 21 in the suburbs of Damascus.

"They are now returning to Damascus," said the statement.

The UN spokesperson office said earlier on Monday that the first vehicle of the Chemical Weapons Investigation Team was deliberately shot at multiple times by unidentified snipers.

In the latest statement, Ban said that he has instructed Angela Kane "to register a strong complaint to the Syrian government and authorities of opposition forces" over the sniper attack, "so that this will never happen and the safety and security of the investigation teams will be secured from tomorrow."

On Aug. 21, the Syrian opposition claimed that some 1,300 people were killed in a chemical weapon attack carried out by the government army on militant strongholds in the suburbs of Damascus. The Syrian government strongly denied the accusation.

The UN investigation team, led by Swedish scientist Dr. Ake Sellstrom, was originally scheduled to spend up to 14 days, with a possible extension, probing the alleged use of chemical weapons in the northern Khan al-Assal town and two other undisclosed locations.

The Syrian government and rebels blame each other for a purported chemical weapons attack on Khan al-Assal on March 19 that killed at least 25 people and wounded 130 others.