By Louis Charbonneau and Michelle Nichols
UNITED NATIONS (Reuters) - U.N. Secretary-General Ban Ki-moon said on Friday he intends to conduct a "thorough, impartial and prompt investigation" into the latest alleged chemical weapons attack in Syria, an issue his top disarmament official will raise in Damascus shortly.
A United Nations statement said U.N. High Representative for Disarmament Affairs Angela Kane was due to arrive in the Syrian capital on Saturday to push for access to the reported attack site for U.N. inspectors, who were already in Syria to investigate previous chemical attack claims.
"It is (Ban's) intention to conduct a thorough, impartial and prompt investigation on the reports of the alleged use of chemical weapons during these attacks," U.N. spokesman Eduardo del Buey said in the statement.
"The secretary-general urges the Syrian authorities to respond positively and promptly to his request without delay, taking into account in particular that the Syrian Government has publicly expressed its own concerns regarding these events," he said.
It is the second day in a row Ban publicly appealed to Syria to grant the U.N. experts access to the alleged attack site.
Syrian President Bashar al-Assad's government is under increasing pressure from Western and Gulf Arab countries and Assad's ally Russia to allow access to the rebel-held site of Wednesday's alleged pre-dawn attack. The opposition Syrian National Coalition has also urged U.N. access.
Assad opponents braved the front lines around Damascus on Friday to smuggle tissue samples to U.N. inspectors from victims of Wednesday's reported mass poisoning, which if confirmed would be the world's deadliest chemical attack in decades.
So far Assad's government has not said whether it will allow chief U.N. chemical investigator Ake Sellstrom's team to visit the site in the suburbs east of Damascus. Syrian U.N. Ambassador Bashar Ja'afari has not responded to a Reuters query about possible access for Sellstrom's team.
The U.N. experts have been in Syria since Sunday to investigate three previous alleged chemical attacks in the country's 2-year-old civil war dating from months ago.
STOCKPILES OF WEAPONS
Assad opponents gave death tolls from the attack ranging from 500 to well over 1,000. The Syrian government has repeatedly denied using chemical weapons.
The United Nations has received a total of 14 reports of possible chemical attacks - one from Syria's government and the rest from Britain, France and the United States.
The U.N. Security Council on Wednesday stopped short of demanding an immediate investigation of the incident by Sellstrom's team, though it did voice support for Ban's intention to pursue a swift inquiry.
The Syrian government and the opposition have accused each other of using chemical weapons, and both have denied doing so. The U.N. inquiry will try to establish only whether chemical weapons were used, not who used them.
Ban said on Monday that if the experts found that chemical weapons had been used then it would be up to "the international community to determine what course of action should be taken to prove ... accountability and what needs to be done."
"Use of chemical weapons is a violation of international law and international human rights law," Ban told a news conference.
The United Nations has been demanding unfettered access in Syria to conduct the investigation. Sellstrom's team consists of experts from the Organization for the Prohibition of Chemical Weapons and the World Health Organization.
Ban appointed Sellstrom to lead the inquiry in March, but diplomatic wrangling and concerns over safety prevented his team from entering Syria until this week.
Syria is one of seven countries that have not joined the 1997 convention banning chemical weapons. Western countries believe it has stockpiles of undeclared mustard gas, sarin and VX nerve agents.
The United Nations says more than 100,000 people have been killed in the Syrian conflict since 2011.
(Reporting by Louis Charbonneau and Michelle Nichols; Editing by Vicki Allen and Eric Beech)