MADRID — Prime Minister Mariano Rajoy of Spain pledged on Saturday to provide “complete transparency” about his own financial assets and those of other politicians in his party to refute what he described as “apocryphal” documents showing that he and others had received regular payouts from a secret parallel account maintained by the party.

In a televised address, Mr. Rajoy said he regretted the damage that the corruption allegations had caused to his image — as well as to the image of his governing Popular Party and Spain as a whole — at a time of economic and social hardship. But he predicted that “this is as far as it will go,” adding, “This party will defend itself.”

Mr. Rajoy also insisted that his party had no connection to the $29 million amassed in Swiss bank accounts by a former party treasurer, Luis Bárcenas, who has been at the heart of the widening corruption scandal. His party, Mr. Rajoy said, “never gave orders to open accounts in a foreign country.”

The prime minister said he would publish online his own tax returns this week. As to the financial rectitude of his colleagues, Mr. Rajoy said “all our tax contributions have been made within the strictest legality over all these years.”