By Ezequiel Minaya

CARACAS, Venezuela--Embattled President Nicolás Maduro lashed out at Washington during a pro-government rally on Monday, days after the U.S. Congress approved penalties against Venezuelan officials amid a deepening economic crisis in this oil-rich country.

"Insolent Yankees of the North!" Mr. Maduro roared at the crowd assembled in this capital for a nationally televised address. "They know where they have to stick their sanctions!"

The latest penalties would freeze any U.S. assets, from homes to the banking accounts, of targeted officials and deny them visas into the country. Though the list of the sanctioned officials wasn't released, Sen. Marco Rubio (R-Fla.), an author of the bill, sought to include several state governors from the ruling socialist party, the country's chief prosecutor and much of the military high command.

With cries of "gringos go home," red-clad backers of the socialist government marched through Caracas, turning their ire toward the U.S. in an event Mr. Maduro used to highlight what he called a global effort to sink Venezuela's economy.

Last week, both the U.S. Senate and the House approved sanctions against officials American lawmakers accused of being responsible for rights abuses in the crackdown on antigovernment protests that left more than 40 dead earlier this year. The White House has signaled that President Barack Obama will sign the bill.

Many economists say that out-of-control spending coupled with stringent currency exchange controls have left the country teetering on the brink of default. In a long speech, Mr. Maduro praised the policies of his predecessor, Hugo Chávez, whose lavish spending during a period of high oil prices made him popular with the poor but who many economists blame for setting the stage for Venezuela's profound crisis.

Mr. Maduro's fiery speech came after a weekend in which he railed against the Obama administration, international ratings firms and economists who have been warning that Venezuela's economy is doomed unless the government embarks on wide-ranging overhauls. Taking together, Mr. Maduro signaled he wasn't close to making significant changes to an economy that Barclays says will contract by 4.4% this year and by more than 6% in 2015.

In a televised interview that aired Sunday with former Vice President José Vicente Rangel, who is a strong supporter of the government, Mr. Maduro said he was in no hurry to scrap a domestic subsidy on fuel that costs the cash-strapped government some $12 billion a year.

He added that he would leave the country's overvalued fixed exchange rate of 6.3 bolivars-per-dollar in place, even though the black market dollar is nearly 30 times more expensive. The president also didn't rule out a default but was a possibility if it could aid an economic recovery.

After Mr. Maduro comments, investors drove Venezuela's benchmark 2027 bonds below 38 cents on the dollar on Monday, its lowest mark since 1998, said Peter Lannigan, head of emerging-markets strategy at broker-dealer CRT Capital Group in Stamford, Conn.

"The government is holding onto policies that will keep it from paying its debt. It's a matter of time," Mr. Lannigan said. "If they keep their current policies in place they will have to default."

Mr. Maduro has sought solace from his allies, who this weekend accompanied him to Cuba for a summit. On Friday, Nicaraguan President Daniel Ortega, whose government has received substantial aid from Venezuela, announced that Mr. Rubio and Rep. Ileana Ros-Lehtinen, (R-Fla.), who had also supported sanctions, would be barred from his country.

"Oh no! My summer vacation plans are ruined!" Mr. Rubio shot back sarcastically in a message on his official Twitter account.

Shannon K. O'Neil, senior fellow for Latin America studies at the Council on Foreign Relations, said that Mr. Maduro's strategy of blaming the U.S. for Venezuela's economic troubles is a "time-proven tactic to deflect attention away from rising inflation, basic goods shortages, and rising crime."

"But it is coming to a point where this government will have to do something drastic," she said.

Venezuela's oil-dependent economy has been battered by the 40% slide in crude prices since July, with the price of a barrel here falling to $57.53 last week. Mr. Maduro, who is struggling to deal with widespread shortages of basic goods and one of the world's highest inflation rates, has seen his approval ratings plummet to 24.5%, the Caracas-based pollster Datanalisis said in a November poll.

The poll also showed that 71.1% of respondents believe Mr. Maduro should leave office before the end of his term in 2018.

"Maduro is acting like a wounded animal, he is lashing out and trying anything that will work," said Christopher Sabatini, senior director of policy at the Council of the Americas in New York. "It looks desperate, it really does. I think that fewer and fewer of the Chavista faithful are going to buy it."

Corrections & Amplifications

This item was corrected Dec. 16, 2014 1233 GMT because it misstated in the seventh paragraph that Barclays says the Venezuelan economy will contract by more than 10% next year. Barclays says it will contract by more than 6%.