The police department's National Fraud Squad launched an investigation on Monday against Israeli websites, including the popular portal Walla, for allegedly posting advertisements for illegal gambling sites. Senior police sources told The Jerusalem Post that Walla CEO Ilan Yisraeli would be called in for questioning in the coming days. Investigators raided Walla headquarters in Tel Aviv, seized documents and detained three employees. Police also detained one employee from the popular Sportline website. Walla is mutually owned by Haaretz and Bezeq International. On Monday, Bezeq International CEO Avi Gabai was appointed Chairman of Walla. Police said that it was "highly unlikely" that Haaretz owner Amos Shoken or owners of Bezeq International would be questioned in the affair. "We would have to first prove that they were directly involved in the content of their websites," police said. Monday's raid came after Attorney General Menahem Mazuz and State Prosecutor Eran Shendar instructed the police to crack down on websites that post advertisements for various gambling sites. Police said that advertisements for the Casino Dealer site and King Solomon appeared on Walla's website. Walla dismissed the accusations and released a statement claiming it was not connected to illegal gambling sites. "This police inspection is part of a larger process to step up the fight against illegal gambling sites on the ï¿½Internet," the company said in released in a statement. "We have no doubt that since we are the largest and most popular site in Israel the investigation began with us. Walla will of course fully cooperate with the investigation." the statement said.