BEIRUT: A war of words is heating up between Hezbollah and Washington, with allegations and counter-allegations flying between the two foes as the crisis in Syria takes its toll on the Shiite militant group.

The cold war between Iranian- and Syrian-backed Hezbollah and the United States -- which blacklists the Lebanese group as a terrorist organisation -- runs back decades.

But with political upheaval in the Arab world at a peak, tensions between the two are skyrocketing.

"This year was not the first time Hezbollah has exposed intelligence networks, whether working for the United States or others, and the United States criminal case against Hezbollah goes back months," said Paul Salem, head of the Beirut-based Carnegie Middle East Center.

"But there's no doubt that, given what's happening in Syria along with the US withdrawal from Iraq ... we're in a phase of high tension in which everyone's raising the pressure on their opponent."

The feud began to deepen earlier this year, when Hezbollah leader Hassan Nasrallah accused the Central Intelligence Agency of planting spies within his party's ranks.

Nasrallah's announcement in June, which the party hailed as a "victory" over the United States, marked the first acknowledgment of infiltration by the movement founded in 1982.

The United States filed a criminal lawsuit against a string of Lebanese financial institutions with alleged ties to Hezbollah on the grounds they were complicit in a massive scheme to funnel hundreds of millions of dollars.

US federal authorities say the companies were part of a scheme to launder hundreds of millions of dollars in profits from narcotics dealing and other criminal activities in order to fund Hezbollah's activities.

But Hezbollah has staunchly denied the charges, with the group's second in command, Sheikh Naim Qassem, accusing Washington this week of waging a smear campaign against a Shiite Muslim group which, he said, would never follow a path "prohibited by religion."

Hezbollah upped the stakes by accusing the "terrorist" United States of being behind twin bombings in the Syrian capital on Friday which left 44 dead and 166 wounded, according to officials.

"These bombings which resulted in the death and injury of dozens of people, mainly women and children, are the specialty of the United States, the mother of terrorism," read a statement released by the movement Friday.

It said the timing of the bombings, which ripped through two security service offices in the Syrian capital, clearly signaled they were a "cowardly, bloody act of revenge" over the US "defeat" in Iraq.

Analysts say the crisis in Syria, which provides Lebanon with its only open border, has dealt a blow to Hezbollah which must now face the possibility of a future without a key regional ally.

And as power structures shift in the Middle East, experts say Western pressure on the Lebanese militant movement will continue to mount as the group risks losing the support provided by the regime of embattled Syrian President Bashar al-Assad.

"The latest US accusations against Hezbollah are ... part of a wider campaign against the Syria-Iran-Hezbollah axis," said Amal Saad-Ghorayeb, author of the forthcoming "The Iran Connection: Understanding the Alliance with Syria, Hezbollah and Hamas."

"We're only going to see more of these accusations," Saad-Ghoryaeb told AFP.

"The United States is aware that ... Hezbollah has already lost some support in the region because of Syria, so now's the time to tarnish its reputation, to move from labeling the group as terrorist to actually criminalising it."