Spain's attorney general said Thursday there are grounds for further investigating allegations of under-the table payments to high-ranking members of the ruling conservative Popular Party.

Following its initial probe, the office of the anti-corruption prosecutor will now work quickly to design a strategy for getting to the bottom of the matter, Eduardo Torres-Dulce told reporters in the northern city of Logroño.

Former PP treasurer Alvaro Lapuerta - predecessor of Luis Barcenas, who is at the center of the scandal - told prosecutors Thursday that the party never operated a slush fund.

Lapuerta, who managed the PP's finances from 1993 to 2008, also denied ever having seen the handwritten ledger attributed to Barcenas that appears to show the payment of extra wages to senior party leaders.

Prosecutors subpoenaed Lapuerta and Barcenas after Madrid daily El Pais published images of extracts from the purported secret ledger, which shows two decades of off-the-books cash payments to party leaders, including current Prime Minister Mariano Rajoy.

"I've never received nor distributed 'black money,' in this party or anywhere else," Rajoy said last weekend at a special meeting of the PP leadership to discuss the scandal, known in Spain as the "Barcenas case."

In statements to prosecutors Wednesday, Barcenas, who stepped down as PP treasurer in 2009, denied the existence of secret accounts and said he was not responsible for the handwritten documents, judicial officials told Efe.

He also provided a handwriting sample that will later be compared and contrasted with the documents published by El Pais.

So far, prosecutors have not linked the PP probe to recent revelations that Barcenas had deposited some 22 million euros (roughly $29.5 million) in Swiss bank accounts. EFE