New Delhi: If you have been receiving missed calls from international numbers, think twice before calling back, says telecom operator Vodafone.

The operator has been witnessing cases wherein people get missed calls from international numbers and when the user calls back they are charged a huge sum for the call.

A Vodafone representative said people in Uttar Pradesh were getting such calls yesterday and today people in Tamil Nadu are receiving these unsolicited calls on mobile phones.

Vodafone said it is investigating the matter. "Some Vodafone customers in Tamil Nadu have been receiving missed calls from international numbers lately. We would like to inform all our customers in Tamil Nadu that this issue has been brought to our notice and we are currently investigating the same," Vodafone India said in a statement.

The company has also asked its over 140 million subscribers in the country to ignore such calls.

"We would like to urge our customers to kindly ignore such calls and not call back on those numbers. In case a customer gets such a call, we request them to call the customer care and report the number to us," it said.

"We want to assure our customers that security is our highest priority. Vodafone takes the safety and security very seriously and we have invested considerable resources to continually evolve our system and improve security," the statement added.