"We stopped working there 18 months ago," he told the Mail on Sunday. "I can't comment any further."
The correspondence is among 2.6 million documents and emails pertaining to Syria that WikLeaks has begun to publish.
The latest tranche to be released showed that Mr Assad provided money to a female aide, Lamis Omar, a doctorate student at the University of Durham.
Emails released earlier this year have demonstrated a surprisingly affectionate relationship between the Syrian president and a number of young women, and Miss Omar wrote effusively about Mr Assad in her emails.
"My life is no longer my own," she declared in one. "I willingly dedicate it for all the meanings I find in you and in all those loved by you. Please allow me to further prove it."
It is unclear whether or not Mr Assad directly paid Miss Omar's university fees.
Brown Lloyd James, an Anglo-American public relations firm also faces embarrassment from the latest disclosures. In may last year, as the violence was worsening, it wrote to Mrs Assad's office proposing that she and her husband burnish their image by embarking on a "listening tour" of Syria.
The firm, founded by former Beatles manager Peter Brown, has previously insisted that it had ended all work with the Syrian government in December, 2010.
A spokesman for the firm said the email was an "unsolicited last-ditch memo" to try to persuade the regime to implement reforms and that no money was received for the advice.
