He said Washington had already launched a non-military campaign using economic, psychological and political means to topple his socialist government and seize control of Venezuela's vast oil reserves.

"We must continue developing the resistance war, that's the anti-imperialist weapon. We must think and prepare for the resistance war every day," the president told hundreds of soldiers assembled at Tiuna Fort, a military base in the capital Caracas, on Sunday.

Wearing an olive-green uniform, red beret and presidential sash, Mr Chávez said Venezuela was locked in "asymmetrical warfare" with the US and that, if it led to combat, soldiers must be prepared to lay down their lives.

"It's not just armed warfare, I'm also referring to psychological warfare, media warfare, political warfare, economic warfare," he said.

There was no immediate response from Washington, but the Bush administration has rejected previous claims that it was plotting to attack its outspoken South American foe.

Mr Chávez's speech came on the eve of a trip to Russia, Belarus and Iran, hosts who share much of his antipathy towards Washington.

He said that while in Minsk he would put "the final touches" to a deal to buy an air defence system with long-range radar and missiles and in Moscow he would discuss the possible purchase of submarines.

Venezuela has recently purchased £1.5bn worth of Russian weapons including 53 military helicopters, 24 SU-30 Sukhoi fighter jets and 100,000 Kalashnikov assault rifles.

Mr Chávez stressed the build-up was a deterrent. "We are strengthening Venezuela's military power precisely to avoid imperial aggressions and assure peace, not to attack anybody."

The air system was purely defensive, he said. "But if somebody comes here, well then, ssssssshhh," he said, imitating the sound of a missile.

The former paratrooper said US dirty tricks were evident in the student-led protests which greeted his decision last month not to renew the licence of RCTV, an opposition-aligned television station. He also said Washington was trying to sabotage the Copa America, a pan-regional football tournament which Venezuela is due to host over the coming weeks.

The Bush administration tacitly backed a coup that briefly ousted Mr Chávez in 2002 and has made no secret of its distaste for a leader who has thrown an economic lifeline to Fidel Castro's Cuba.

Mr Chávez claimed there have been numerous US-sponsored attempts on his life since the coup, but he has not provided details.