The Lebanese have also covertly received more land-to-land Scud-D missiles from Syria, the New York Times reported, despite assurances given by Syrian president Bashar al-Assad that Damascus was not channelling arms to the Lebanese militant group.
The Times said the Obama administration had lodged a confidential protest with accusing Syria of "doing precisely what it had denied doing".
Quoting leaked United States diplomatic cables, the paper said Hezbollah's arsenal now include upto 50,000 rockets and missiles, including 40 to 50 Fateh-110 missiles capable of reaching Tel Aviv and most of Israel and 10 Scud-D missiles.
Pentagon says the huge flow of arms to Hezbollah had raised fears of a conflict with Israel, which may engulf the whole region.
Wielding surveillance photos and sales contracts, American diplomats have confronted foreign governments about shadowy front companies, secretive banks and shippers around the globe, according to secret US state department cables obtained by WikiLeaks and made available to several news organisations.
American officials have tried to block a Serbian black marketer from selling sniper rifles to Yemen. They have sought to disrupt the sale of Chinese missile technology to Pakistan, the cables show.
But while American officials can claim some successes -- Russia appears to have deferred delivery of the S-300 air defence system to Iran -- the diplomats' dispatches underscore how often their efforts have been frustrated in trying to choke off trade by Syria and others, including Iran and North Korea.