Russian President Dmitry Medvedev (r) and Venezuelan President Hugo Chavez exchange documents during a signing ceremony at the Barvikha presidential residence, outside Moscow, 10 Sep 2009The United States said Monday an ongoing military buildup by Venezuela poses a serious challenge to regional stability. The comments follow an announcement that the Caracas government of President Hugo Chavez has received a line of credit from Moscow to purchase Russian tanks and anti-aircraft missiles.

The State Department says Venezuela's recent arms acquisitions far outpace those of any other South American country.  The Obama administration is calling for more transparency by the Chavez government and assurances that its weapons are not on-passed to regional insurgents or other non-state actors.

The comments from State Department Spokesman Ian Kelly were the most pointed to date by the administration on the Venezuelan arms buildup, which was a subject of frequent statements of concern by the Bush administration.

Venezuelan President Hugo Chavez said Sunday his government has received a $2.2 billion line of credit from Moscow to buy 92 Russian-made T-72 battle tanks as well as a long-range Russian anti-aircraft missile system.

Kelly told reporters the United States has broad concerns about Venezuela's desire to increase its arms purchases, which he said poses a "serious challenge to stability" in the Western Hemisphere.

"What they are looking to purchase, and what they are purchasing, outpaces all other countries in South America, and of course we are concerned  about an arms race in the region," said Ian Kelly. "And we urge Venezuela to be transparent in its purchases, and very clear about the purposes of these  purchases. And we're also very concern that they put in place very clear procedures and safeguards that these arms are not diverted to any irregular or illegal organizations in the region."

Kelly's mention to irregular organizations was an apparent reference to leftwing FARC guerillas in Colombia, to which the Venezuelan government has been accused by its neighbor of providing small arms and occasional safe-haven.

Venezuelan President Chavez said he is buying more arms because his government feels threatened by the U.S.- Colombian agreement last month to give U.S. forces access to several Colombian military bases to combat regional drug trafficking and terrorism.

The Obama administration says the agreement, prompted in part by the denial of further U.S. access to an air base in Ecuador, is not directed against any other country and would not mean permanent U.S. bases in Colombia or a sizeable increase in the American presence there.

Under questioning here, Kelly also said the United States will be looking closely into media reports Venezuela might get technical help on civilian nuclear power from Iran, which has developed close ties with the South American state and is accused by the United States and others of seeking nuclear weapons.

He said Venezuela, as a signatory of the nuclear Non-Proliferation Treaty, has specific obligations for transparency and disclosure for any civilian nuclear program.