Updated

The government detained the striking crew of a tanker and moved the gasoline-laden vessel toward port Saturday as the nationwide work-stoppage against President Hugo Chavez dried up Venezuela's gas supplies.

Leaders of the 20-day-old general strike accused Chavez of using a Cuban crew to pilot the Pilin Leon, which had been moored offshore after the crew joined the strike. Carlos Fernandez, a strike organizer and president of the Fedecamaras business chamber, said the use of Cubans "violates national sovereignty."

A source at the Cuban Embassy in Caracas, speaking on condition of anonymity, denied the claim, calling it a "lie." State TV said Venezuelans were piloting the ship. Chavez's rivals often accuse the president of being too close to communist Cuba.

Government security forces detained the Pilin Leon's captain and crew Friday night, Cuiro Izarra, international commercial manager of the state oil company, told Globovision TV. On Saturday, the vessel was heading toward a port in Maracaibo Lake.

The takover of the vessel came as gasoline supplies in Venezuela began drying up Saturday, creating a specter of food shortage. Britain joined the United States and other nations in urging its citizens to leave Venezuela, fearing shortages will spark violence.

The strike, launched Dec. 2 to force Chavez from office, has crippled oil production in the world's fifth-largest exporter of crude and sent global oil prices climbing.

Defense Minister Jose Luis Prieto went on TV to urge all striking oil workers to obey a Supreme Court ruling ordering on them to immediately return to work. Otherwise, he said, they "will be subject to sanctions."

Most gas stations were shut and the National Guard stationed at the few that were open tried to keep impatient motorists in lines that were blocks long.

Sitting in his beat-up bus, which stood out of gas and idle in a working class neighborhood, Rafael Perez waited for a friend to arrive with fuel.

"I don't sympathize with any side, but this strike is endangering all of us," Perez muttered. "In a situation like this, we all lose."

Afraid the gasoline shortage could affect the availability of food, many people rushed to open-air street markets to stock up on supplies.

Leaders of the strike vowed to maintain the stoppage until Chavez resigns or calls early elections. The president's opponents say he has mismanaged the economy, widened class divisions and intends to impose a Cuban-style leftist state in this South American country of 24 million.

The government is insisting that Chavez -- who constitutionally is not obligated to submit to a referendum on his rule until next August -- would not bend.

Protests this week for and against Chavez have been mostly peaceful, but there is increased worry about the security situation.

Britain asked citizens only with urgent business to remain in Venezuela, saying a gas shortage might leave food stores bare and might in turn trigger disturbances," the Foreign Office in London said.

The Foreign Office said it was withdrawing families of British diplomats and nonessential embassy staff. The United States, Canada and Germany have made similar recommendations.

As the strike wore on, the resolve among some of Chavez's opponents seemed to strengthen. Already, merchants, by keeping their stores closed, have sacrificed profits during the peak Christmas buying season.

"I have faith that this strike will be a success with Chavez leaving," said Fabio Valencia, a taxi driver who had a quarter tank of gasoline left. "I voted for him, and now I regret it."

Under Chavez, Venezuela's economy shrank 6 percent in the first nine months of this year, unemployment is at 17 percent and inflation at 30 percent. Tensions between rich and poor are high.

Chavez, a former army paratroop commander who led an unsuccessful coup in 1992, was elected by a landslide in 1998 and re-elected in 2000, promising to help the nation's poor.

His popularity has dropped to about 30 percent, according to a recent opinion poll. But in the shanty towns ringing Caracas his popularity is as high as 45 percent.