|Migrants wait for residence permits to enable them to go to France, at the police station of Ventimiglia [EPA]
France has shut its border to trains from Italy in an attempt to stop north African migrants and political activists from entering the country.
The action drew a formal protest on Sunday from Rome and accusations it was violating European principles.
A group of French and Italian activists had planned to board what they had dubbed The Train of Dignity in the Italian border town of Ventimiglia in support of migrants trying to cross the border.
About 60 mainly Tunisian migrants were at the station seeking passage to France, and were given sandwiches and drinks by support groups.
Italian railway and border police said France was preventing all trains passing the Ventimiglia-Menton border.
Franco Frattini, Italy's foreign minister, instructed the country's ambassador in Paris to express "the firm protest of the Italian government to the French authorities", a foreign ministry statement said.
France's actions appear to be "illegitimate and in clear violation of general European principles", it said.
Speaking to Al Jazeera from Rome, Maurizio Caprara, the diplomatic correspondent for Corriere Della Sera, an Italian newspaper, said both governments were being influenced in their actions by upcoming election campaigns.
Caprara said: "The French have an electoral campaign in 2012, Nicolas Sarkozy has the problem of Jean-Marie Le Pen and his Front National, that is strongly against foreign immigration.
"And in Italy we will have a partial term of administrative elections in which the Northern League is particularly active against this flow of immigration that recently came in Italy."
Italy has complained about being "left alone" by European Union partners to deal with thousands of mainly Tunisian migrants who have arrived on its southern island of Lampedusa in recent weeks, fleeing political turmoil in North Africa.
It has began issuing migrants with temporary permits allowing them to leave Italy to travel to other destinations in Europe, a policy which has been criticised by several of its partners, including France and Germany.
Some of the countries in the 27-nation EU are worried that offering shelter to too many migrants will encourage more to attempt illegal entry to Europe.
Roberto Maroni, Italy's interior minister, said in a television interview on Sunday that France's stance was "incomprehensible" and "tough and unjustified towards Italy".
He said he hoped "friendly relations" could be re-established with France at a summit meeting on April 26, where immigration will be near the top of the agenda.
Hundreds of Italian demonstrators gathered at the station at Ventimiglia to protest against France's actions, chanting anti-French slogans and trying to persuade police to allow them to demonstrate outside the French consulate at Menton.
A French interior ministry spokesman told Italian news agency ANSA that the decision to block the trains was a temporary measure taken for safety reasons due to the demonstrations around the station.
Italian protests against France crossed the political divide, with Mario Tullo, a politician from the opposition Democrats of the Left party saying its decision to block the trains was "illegal" and "absurd", and contravened EU treaties.
Earlier this month, the interior ministers of France and Germany agreed to set up joint patrols off the Tunisian coast to deter would-be migrants and Rome has also pledged assistance to Tunisia to try to halt the flow.