In one cable given to the paper by WikiLeaks, Syrian President Bashar al-Assad is reprimanded for supplying sophisticated weapons to the Shiite terror group Hezbollah one week after providing assurances he would not.
"In our meetings last week it was stated that Syria is not transferring any 'new' missiles to Lebanese Hezbollah," said the cable sent by US Secretary of State Hillary Clinton in February.
"We are aware, however, of current Syrian efforts to supply Hezbollah with ballistic missiles. I must stress that this activity is of deep concern to my government, and we strongly caution you against such a serious escalation."
A senior official at the Syrian foreign ministry rejected the allegations, but nine months on the flow is unchecked, The New York Times said, citing Pentagon officials.
The New York Times report said that according to an American cable, the Syrian official argued that Hezbollah would not take military action if not provoked and expressed surprise at the stern American protest. The complaint, he said, “shows the US has not come to a mature position (that would enable it) to differentiate between its own interests and Israel’s.”
US diplomats, the cables reveal, are constantly confronting foreign governments about shadowy front companies and banks suspected of involvement in the illegal arms market but successes are rare.
Diplomats have attempted to stop a Serbian black marketeer selling sniper rifles to Yemen, China selling missile technology to Pakistan, and India exporting chemicals that could be used to make poison gas.
They expressed repeated concern that the Palestinian terror group Hamas was receiving weapons on huge cargo planes operated by Sudan's Badr Airlines.
'Newly fortified Hezbollah'
Despite Sudan's insistence the cargo was agricultural machinery, the United States asked other countries in the region to deny overflights but Yemen declined, according to a February 2009 cable released to The New York Times.
In another, dated April 2009, Egypt accuses Iran of providing $25 million a month to Hamas and links Tehran to a Hezbollah arms smuggling cell.
The cables shed light on how North Korea uses the Korea Mining Development Corporation as a front for its operations, relying on steel and machinery parts from China, Japan and Switzerland and Taiwan.
Diplomatic protests about North Korea's sale to Sri Lanka of rocket-propelled launchers and to Yemen of Scud missile launchers went unheeded in early 2009, cables show, according to The New York Times.
"Chinese banks have been targeted by North Korea as the main access point into the international financial system," said a July 2009 cable from senior US Treasury official Stuart Levey.
But the principal concern appeared to be Hezbollah and Syria, who President Barack Obama has sought to engage as part of his efforts to foster a wider peace in the Middle East.
"Syria's determined support of Hezbollah's military build-up, particularly the steady supply of longer-range rockets and the introduction of guided missiles could change the military balance and produce a scenario significantly more destructive than the July-August 2006 war," said a November 2009 cable from diplomatic staff in Damascus.
A particularly grave concern was that Hezbollah had been provided with sophisticated Fatah-110 missiles, which are deadly accurate and would have the capacity to strike most of Israel, including Tel Aviv.
The New York Times said that, according to a Pentagon official, Hezbollah's arsenal now includes some 50,000 rockets and missiles, including some 40 to 50 Fatah-110 missiles and 10 Scud-D missiles.
According to the New York Times, the cables note that Israeli officials told American officials in November 2009 that if war broke out, they assumed that Hezbollah would try to launch 400 to 600 rockets at day and sustain the attacks for at least two months.
"The newly fortified Hezbollah has raised fears that any future conflict with Israel could erupt into a full-scale regional war," the report said.
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