A spokesman for the US state department said on Monday that Washington is concerned "about Venezuela's stated desire to increase its arms build-up, which we think poses a serious challenge to stability in the Western Hemisphere."
Ian Kelly called on Caracas to abide by its its nuclear non-proliferation obligations.
Venezuela has bought over $4bn of weapons from Russia in recent years, including 24 Sukhoi fighter jets.
It was not immediately clear when Venezuela would receive the new weapons or how much they would cost.
Critics say Venezuela is sparking an arms race in South America, but Chavez says he is modernising the military for defensive purposes.
The country is embroiled in a diplomatic crisis with Colombia over a deal to allow troops from the US access to more bases in the neighbouring country to fight drug traffickers and leftist fighters.
Chavez, a fierce critic of US foreign policy, says the Colombian bases plan could be used to launch an attack on Venezuela and increases the risk of war on the continent.
"Let me be clear, Venezuela has no plans to invade anybody, or to be aggressive towards anybody," Chavez said on his show.
Last year, the former soldier ordered tanks to the border with Colombia in a dispute over a Colombian bombing raid in Ecuadorean territory.
Chavez said Venezuela was now buying 92 Russian T-72 tanks along with several types of missiles, including the Buk-M2 and S-300, to build an air-defence system.
The S-300, also known as the SA-20, is considered one of the most effective surface-to-air anti-aircraft systems and is capable of tracking 100 targets at once.
It can be used with missiles that have a range of about 200km and can engage six targets simultaneously.
"With these rockets it's going to be very difficult for foreign planes to come and bomb us," Chavez said.
Russia signed a contract in 2007 to supply Iran with the S-300 system but has dragged its feet on delivering the weapons after Washington and Israel expressed fears it would be used to protect nuclear facilities from attack.
Last week, Moscow dismissed rumours that a ship supposedly loaded with timber that went missing in the Atlantic in July had really been carrying a cargo of S-300s for Iran.
Chavez repeated on Sunday his commitment to developing nuclear power for peaceful purposes with the help of Russia and reiterated he was opposed to nuclear weapons.