Riot police deployed outside the Bar du Palais in Bayonne, in the southwestern Basque region, where Sarkozy was on the campaign trail to seek re-election in a presidential vote in April and May.
Some of the protestors jeered and booed and threw eggs at the bar while others shouted “Nicolas kampora!”, which in the Basque language means “Nicolas get out!”, and threw out tracts calling for more Basque autonomy.
The president was booed from the moment he got out of his car in the centre of the city and was followed by a jeering crowd all the way to the bar, where he had been scheduled to meet with local voters.
He remained in the bar for an hour while police held off the protestors, some of whom were brandishing the electoral programme of the Socialist candidate Francois Hollande.
Sarkozy, who was due in Brussels later Thursday for a European Council meeting, condemned the incident and put the blame partly on the party of his frontrunning rival.
“I am saddened to see Hollande’s Socialist militants associating with (Basque) separatists in violent protests to terrorise ordinary people who want just one thing: to meet and talk with me,” he said.
His campaign spokeswoman Nathalie Kosciusko-Morizet accused the Socialists of organising “street protests” against the president.
But Manuel Valls, a senior member of Hollande’s campaign team, said that while his boss condemned any violence, no Socialist was involved in the Bayonne incident.
The Basque region straddles southwestern France and northern Spain. ETA, a separatist movement which called an end to its armed struggle last year, is blamed for 829 deaths during a four-decade campaign of shootings and bombings for an independent Basque homeland.
Hollande was Thursday holding his third major campaign rally in the eastern city of Lyon.
An opinion poll published Tuesday by IFOP said the Socialist would take 28.5 percent of the vote in the first round of the presidential election in late April, against 27 percent for President Nicolas Sarkozy.
Far-right National Front leader Marine Le Pen would come in third with 17 percent, it said.