Bulgaria and Norway have become new focal points of a global hunt for who supplied Hezbollah with the thousands of pagers that exploded in Lebanon this week in a deadly blow to the militant group.
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Security sources said that Israel was responsible for the explosions on Tuesday that killed 12 people, injured more than 2300 and raised the stakes in a growing conflict between the two sides.
Israel has not directly commented on the attacks.
How and with whose help the pager attack was carried out was not yet known although so far there were possible leads in Taiwan, Hungary and Bulgaria.
It is not clear how and when the pagers were weaponised so they could be remotely detonated.
The same question remains for the hundreds of walkie-talkies used by Hezbollah that exploded on Wednesday in a second wave of attacks.
One theory is that the pagers were intercepted and hooked up with explosives after they left factories.
Another is that Israel orchestrated the whole deadly supply chain.
Bulgarian authorities said on Thursday that its interior ministry and state security services had opened an investigation into a company's possible ties.
They did not name the company they were investigating.
Local media reports said Sofia-based Norta Global Ltd had facilitated the sale of the pagers to Hezbollah.
Citing security sources, broadcaster bTV reported that 1.6 million euros ($A2.6 million) related to the transaction passed through Bulgaria and was sent to Hungary.
Reuters could not immediately confirm the claim.
Emails sent to a Norta email listed on Bulgarian company registration records were returned as undeliverable.
The firm's founder declined to comment.
Images of destroyed pagers analysed by Reuters showed a format consistent with devices made by Taiwan's Gold Apollo.
Gold Apollo said on Wednesday that the pagers were made by BAC Consulting, a company based in the Hungarian capital Budapest.
The owner and CEO of BAC Consulting, Cristiana Barsony-Arcidiacono, did not return multiple requests for comment by phone and text message.
On Wednesday, she told NBC News that her company worked with Gold Apollo but that she had nothing to do with the making of the pagers.
"I am just the intermediate. I think you got it wrong," she told NBC.
Hungarian news site Telex reported that the sale was facilitated by Norta Global Ltd, citing sources.
Norta's Bulgarian headquarters are registered at an apartment building in the capital Sofia that is also home to nearly 200 other companies, according to a local company registry.
There was no sign of Norta.
A lawyer, Vladimir Kuzmanov, who said he represented the company, was present at the address but declined to respond to questions when approached by Reuters on Thursday.
Content on Norta Global's website, globalnorta.com, was deleted on Thursday.
The website previously had English, Bulgarian and Norwegian language versions and advertised services including consulting, technology integration, recruitment and outsourcing.
"Are you looking for an agile company to help you succeed or to find that tech solution just right for you? Look no further," the website had said, according to copies of the website reviewed by Reuters before it was altered.
Norta's founder, Rinson Jose, is based in Norway.
He declined to comment on the pagers when reached by phone and hung up when asked about the Bulgarian business.
His neighbours in a quiet suburb of Oslo said they did not know much about him.
Amund Djuve, the CEO of DN Media, where Jose currently works, told Reuters he was aware of the reports and had alerted the police and security services.
He said that Jose was travelling to the United States.
"We are taking these matters very seriously," Djuve said.
Oslo police said it had initiated "preliminary enquiries into the information that had come to light".
Norway's domestic intelligence agency PST said it was aware of the situation and declined to comment further.
There was no evidence of a link between DN Media and Norta.
Barsony-Arcidiacono of BAC Consulting, the Budapest-based company that was also linked to the sale of the pagers, vacated her apartment in Budapest on Wednesday, a neighbour told Reuters.
Her door was ajar on Wednesday but closed on Thursday morning, a Reuters reporter at the scene said.
No one answered the doorbell.
A Lebanese security source told Reuters that Hezbollah believed it was ordering the pagers from Gold Apollo and that they were produced in Asia and not Europe.
The source said Hezbollah considered it much easier for Israel's Mossad spy agency to operate in Hungary.
"It is possible that the Mossad created a European company," the source said.
Australian Associated Press