Explosive pagers used by Hezbollah had been modified by Israel 'at production level', Reuters told by Lebanese security sources

Israel's Mossad spy agency planted a small amount of explosives inside thousands of pagers ordered by Hezbollah months before the devices exploded, a Lebanese security source has told the Reuters news agency.

The senior source said the militant group had ordered 5,000 beepers which several other sources said were brought into Lebanon in the spring.

The same source claimed the devices had been modified by Israel's spy service "at the production level".

A second security source told Reuters up to 3g of explosives were hidden in the new pagers that went "undetected" by Hezbollah for months.

Details from the Reuters report are similar to one by the New York Times, which cited American and other officials.

Images of the destroyed devices analysed by Reuters showed a format and stickers consistent with the AR-924 model of pagers with Gold Apollo branding - a Taiwan-based company.

The firm's founder Hsu Ching-Kuang said the devices were actually made under licence in Europe by a firm called BAC, using the Gold Apollo name.

In a statement given to Sky News in Taiwan, the company said: "Apollo Gold Corporation has established a long-term private label authorisation and regional agency cooperation with BAC.

"According to the agreement, we authorise BAC to use our brand trademark for production sales in specific regions, but the design and manufacturing of the products are entirely handled by BAC."

Apollo Gold said the European firm was based in Hungary's capital Budapest, but declined to give further details.

The model, like other pagers, wirelessly receives and displays text messages but cannot make telephone calls.

Nine people were killed and thousands seriously injured in Tuesday's explosions in different parts of Lebanon, the country's health minister said.

Firas Abiad said 200 of the 2,750 wounded were in a critical condition.

Lebanese officials laid the blame on "Israeli aggression", while Hezbollah promised to retaliate, insisting Israel would receive "its fair punishment" for the blasts.

The Israeli military, which has been engaged in cross-border fighting with Hezbollah since the start of the war in Gaza in October last year, has refused to respond to questions about the detonations.

Experts broadly agree the blasts do not look like a typical lithium battery fire.

Keren Elazari, a hacker and security researcher at Tel Aviv University, told Sky News: "There is no remote hacking capability that could generate that kind of kinetic explosion... some sort of a physical explosive component was probably part of the equation."

Bomb disposal expert and former British army officer Chris Hunter said his initial theory - based on injuries - suggests the blasts are "consistent with one to two ounces of high explosive".

"We've seen this sort of similar MO [particular method] with mobile devices before," he said, pointing to the assassination of Hamas master bomb maker Yahya Ayyash, whose mobile phone had been laced with a small amount of explosives.

Hezbollah fighters would have considered pagers a lo-fi, harder-to-infiltrate alternative to mobile phones, according to Sky News's Middle East correspondent Alistair Bunkall.

It comes after Hezbollah leader Hassan Nasrallah warned the group's members in February not to carry mobile phones because Israel could use them to track their movements.

-SKY NEWS