President Nicolas Sarkozy has ordered the head of the French train authority to get Eurostar traffic moving again by Tuesday.
Eurostar has suspended traffic pending tests aimed at determining what caused five trains to get stuck inside the Channel Tunnel late Friday, trapping more than 2,000 people for hours in claustrophobic conditions.
On Monday, Sarkozy called in SNCF President Guillaume Pepy and ordered him to get traffic moving again by Tuesday and present measures to assure such incidents don't happen again.
The French government on Monday announced a thorough investigation into the shutdown of the Eurostar, as the suspension of the only passenger rail link between Britain and continental Europe entered its third day, hitting holiday travel plans for some 55,000 people.
The company tentatively identified freezing and snowy weather in northwestern France as the cause. It has said no trains will run on Monday pending the tests, and a spokeswoman said she could not guarantee that service would resume Tuesday. More snow was forecast Monday night and Tuesday in Calais, where the train ducks into the tunnel on the French side of the Channel.
French Transport Minister Dominique de Bussereau called the situation "unacceptable" and promised a thorough investigation into its causes.
"We cannot imagine that this mode of transport, which is fundamental between France and England, between England and Belgium and the rest of continental Europe doesn't work because it's snowing outside," Bussereau said on Europe-1 radio, speaking from Beijing where he is on an official visit.
"Therefore, the government is asking, number one, for explanations, number two, we are going to do our own probe, number three, we demand that measures be taken so this does not happen in the future."
Ecology Minister Jean-Louis Borloo also lashed out against Eurostar, calling the situation "absolutely unbelievable" and saying he was meeting later Monday with the heads of Eurotunnel and of France's SNCF railway operator, which owns a majority stake in Eurostar.
He added he was upset with the company's treatment of passengers throughout the incident.
"You can't treat people like that, (leaving them) without information," he told BFM television.
Meanwhile Monday, Eurostar announced it had commissioned an independent review into the problems. In a statement, it said it had named one French and one British expert to lead the review.
The company had previously said it had traced the problem to "acute weather conditions in northern France," which is experiencing its worst winter weather in years.
Eurostar commercial director Nick Mercer said three test trains sent through the Channel Tunnel on Sunday ran successfully, but that it became clear that the especially bad weather meant that snow was being sucked into the trains in a way that has never happened before.
"The engineers on board have recommended strongly that, in light of further snowfalls that are happening tonight, we make some modifications to the trains on snow shields to stop snow being ingested into the power car," he told the BBC.
With a huge backlog of passengers building, Eurostar is blocking any sales until after Christmas and Eurostar chief executive Richard Brown has warned that services may not be back to normal for days.
For those seeking alternative routes between Paris, Brussels and London, the winter weather was dealing out more bad news.
Nearly half of all flights out of Paris' Charles de Gaulle and Orly airports were cut Sunday through mid-afternoon, with more cancellations forecast for Monday. Belgium was also badly hit, with passengers in Brussels lining up for hours in an effort to rebook flights.