"Why can't Venezuela enter Mercosur? The order comes from Washington," Chavez said during his weekly television and radio program "Hello, President."
Venezuela signed an agreement to join Mercosur over a year ago, but its entry has not been ratified by Brazilian and Paraguayan congressmen.
The United States believes that Chavez sees Mercosur as a way for South American nations to unite against U.S. economic and political influence in the region.
Chavez said Brazilian and Paraguayan lawmakers' delay to vote to ratify Venezuela's Mercosur membership is caused by the U.S. pressure. Meanwhile, he praised Brazilian and Argentine leaders for defying the U.S. attempt to isolate Venezuela.
Chavez had threatened to withdraw its bid if it fails to enter the bloc by September, but he backtracked in his speech, saying that he did not give "an ultimatum."
The Venezuelan president also said he is interested in holding talks with Colombian leftist guerrilla groups to advance an accord to end over four decades of war in Colombia.
The Venezuelan leader is to visit Buenos Aires on Monday with promises to help Argentina financially by buying millions of dollars' worth of debt bonds, the Venezuelan embassy in the Argentine capital said.
Chávez also is visiting Uruguay, during a tour taking him to Argentina, Bolivia and Ecuador, Friday said Uruguayan government sources and diplomats.
"President Chávez is coming to Montevideo on August 7-8," the official source said under condition of anonymity.
"The agenda has not been defined, but bilateral topics will be addressed," he added.
Mercopress