The Trump administration has frozen all Venezuelan government assets in a dramatic escalation of tensions with socialist leader Nicolás Maduro, who has stubbornly clung to power in the face of mounting international pressure.

The ban on Americans doing business with Venezuela's government takes effect immediately. An executive order signed by President Donald Trump on Monday justified the move by citing Maduro's continued "usurpation" of power and human rights abuses by groups loyal to him.

While the order falls short of an outright trade embargo, it represents the most determined U.S. action to remove Maduro since the Trump administration recognized opposition leader Juan Guaidó as Venezuela's rightful leader in January. As such, it places Venezuela on par with adversaries such as Cuba, Syria, Iran and North Korea, who have also come under strident U.S. measures.

Previous sanctions have targeted dozens of Venezuelan government insiders as well as the South American nation's oil industry, the source of almost all of its export earnings.

As part of the executive order, Americans will be banned from engaging in transactions with anyone determined to be assisting Maduro or his government. The same Maduro supporters will also be banned from entering the U.S.

Exceptions will be allowed for the delivery of food, medicine and clothing. Transactions with Venezuela's still sizable private sector do not appear to be affected either.

The executive order comes the day before Trump's national security adviser John Bolton and U.S. Commerce Secretary Wilbur Ross represent the United States at the International Conference for Democracy in Venezuela.

The conference is being attended by representatives from more than 50 nations that recognize Guaidó as Venezuela's president and consider Maduro's re-election last year to be fraudulent.

Moments after the executive order was announced, Bolton tweeted that he was looking ahead to what he hopes will be a "productive" day in Lima.