Catalonia's leader accused the Spanish ruling party on Tuesday of waging an "all-out dirty war" to derail his campaign for nationhood ahead of weekend elections.
Days before snap elections on November 25, Artur Mas denied as "libel and slander" a newspaper's allegations that he had a Swiss bank account beyond the reach of the taxman.
Mas's nationalist alliance, Convergence and Union, has sued for libel against the conservative daily El Mundo, which published the allegations citing a police report, he said.
In open defiance of Madrid, the Catalan political chief is promising voters a referendum on self-determination as he fights for an absolute majority in the region of 7.5 million people.
Prime Minister Mariano Rajoy earlier denied Mas' allegations that the state was behind the allegations in an effort to destroy him and derail his plan to make Catalonia a sovereign state.
But Mas demanded on Tuesday to know who was behind the police report that reportedly contained the allegations.
"In that case let (Rajoy) tell me who made this report. Who was responsible for ordering it? Who is responsible? It cannot be someone who does not belong to the state. The police depend on the government and it is led by Rajoy," he told Catalan television station TV3.
Mas said he would refuse to even consider an alliance with Rajoy's Popular Party after the vote because it had opposed the referendum and "they are making an all-out dirty war".
Latest polls show Mas' alliance heading for a win but falling short of the absolute majority he is seeking.
Mas has vowed to embark in January on the road towards a referendum, saying it could take four years. He warned that the nationalist cause would be "weakened", however, if he failed to win an absolute majority.
Surveys this weekend showed Mas' alliance winning 60-64 of the 135 seats in parliament with Rajoy's Popular Party and the opposition Socialists fighting for second place.
In a referendum on "self-determination," Catalans would vote in favour by 46 percent to 42 percent, according to a survey in leading daily El Pais.
Rajoy has called for unity as Spain fights an economic crisis that has left one in four workers unemployed, warning that the separatist bid will harm all Spaniards.
"Catalans are not going to buy a train ticket with no return journey," the Spanish prime minister said Sunday.
But Catalonia, which is proud of its distinctive language of culture, feels it gets a raw deal because Madrid levies far more in taxes than it returns to the region.
At the same time, it is slashing spending to curb its deficit, it has the biggest debts in Spain, equal to 22 percent of its annual output, and it has had to go cap in hand to Madrid for a rescue loan.
Emboldened by huge protests in Barcelona demanding independence on Catalonia's national day, September 11, Mas called the snap election when he failed to secure greater taxing powers for the region.
Though now at the forefront of the separatist campaign, Mas had previously been seen as a moderate nationalist and even now he avoids calling for complete independence.