No pagers used in the Lebanon attack were imported to, exported from, or made in Bulgaria, the country's state security agency DANS has said.

Yesterday, Bulgarian authorities said its interior ministry and state security services had opened an investigation into a company's possible link to the sale of pagers to Hezbollah, which exploded earlier this week in a coordinated attack.

It remains unclear how and when the pagers were tampered with to remotely detonate - with the same questions hanging over the hundreds of walkie-talkies used by Hezbollah that exploded on Wednesday.