Warplanes, tanks, and 200,000 troops of the National Bolivarian Armed Forces (FANB) were deployed along with 700,000 reserves and civil militia members as the exercises formally launched on Saturday.
"Against the belligerent threats of the United States, all Venezuelans between the ages of 18 and 60 are required to contribute to the integral defence of the nation," said an announcement broadcast on state television.
"A complete menu of training skills was being offered to allow ordinary Venezuelans to be able to resist in case of a US invasion, as well as an internal subversion from the opposition," Al Jazeera's Lucia Newman said, reporting from Venezuela's largest military academy in Caracas.
Trump warned on August 11 the US was mulling a range of options to solve Venezuela's political crisis, "including a possible military option if necessary".
Top US officials later played down the threat. "No military actions are anticipated in the near future," said National Security Advisor HR McMaster on Friday.
But tensions surged again when the White House made good on the sanctions threat on Friday, unveiling its first-ever such measures to target Venezuela as a whole, rather than just Maduro and his inner circle.
The sanctions, which Trump signed by executive order, prohibit American financial institutions from providing new money to Venezuela or the state oil company, PDVSA, and could make it harder for Maduro to raise badly needed cash to prevent a debt default.
They also restrict the Venezuelan oil giant's US subsidiary, Citgo, from sending dividends back to Venezuela and ban trading in two bonds the government recently issued to circumvent its increasing isolation from Western financial markets.
Maduro decried the US measures during a national address on Friday.
"Nobody can use economic and financial measures to impose their political will over a country," he said. "Economic war, pressures and blackmail are illegal. They ratify an imperial road of aggression."
Defence Minister Vladimir Padrino Lopez said the armed forces support "all measures being implemented to counter the financial blockade".
In an address at one of the exercises near the capital Caracas, he told assembled troops the drills were "for the defence of the whole country" against "imperial aggression".
Lopez said the exercises would include rifle practice on Saturday and combat manoeuvres on Sunday.
The US embassy in Caracas advised its citizens in the country to stay away from the military exercises, warning of the risk of action by armed civilian loyalists.
Venezuela was gripped by months of anti-government protests over growing anger against Maduro.
The opposition, who demand new elections, say Maduro is turning the crisis-hit country into a dictatorship.
Maduro says the violence and the economic crisis are a US-backed conspiracy.
Diplomatic tensions increased last month when a legislative superbody called the Constituent Assembly was elected at Maduro's behest. It has the power to legislate, bypassing the opposition-controlled congress.
Source: Al Jazeera and news agencies