(Reuters) -Singapore Telecommunications Ltd said on Monday its unit Dialog faced a cyber attack that potentially affected 1,000 current and former employees and fewer than 20 clients, weeks after a massive data breach at another Australian unit - Optus.

The breach at Optus, Australia's second-largest mobile operator, late last month compromised data of up to 10 million customers, triggering an overhaul of consumer privacy rules to facilitate targeted data sharing between telecommunication firms and banks.

Singtel said on Monday the attack on Dialog, an Australia-based information technology services consulting firm, was first detected on Sept. 10.

Shares of Singtel were down 1.6%, as at 0315 GMT.

The Singapore-based telecom firm assured that Dialog's systems were completely independent of Optus and information technology unit NCS, and that there was no evidence of any link between the incidents of data breaches at Dialog and Optus.

Last week, Dialog realised "a very small sample" of its data, including some employee personal information, had been published on the dark web.

Singtel had acquired Dialog in April for A$325 million ($206.57 million).

($1 = 1.5733 Australian dollars)

(Reporting by Sameer Manekar in Bengaluru; Editing by Sherry Jacob-Phillips)