Prime Minister Ariel Sharon once had a close business relationship with the former father-in-law of an Israeli businessman released in a controversial prisoner swap with Lebanese guerrillas, an Israeli newspaper reported Wednesday.

The daily Maariv said that the connection spurred Sharon's strong push to secure the release of Elhanan Tannenbaum (search), a shady reserve colonel held captive by Hezbollah for more than three years.

Sharon told reporters Wednesday he did not know that Shimon Cohen, who once helped manage Sharon's farm, was Tannenbaum's former father-in-law. In any case he had not spoken to Cohen in decades, he said.

"I didn't know his family ties, I still don't know today how many sons-in-law or daughters-in-law or former sons-in-law he has," Sharon said.

The new revelation comes as Sharon faces a series of other corruption allegations. Real estate mogul David Appel (search) was indicted in January on charges of bribing Sharon. Police are also investigating allegations Sharon obtained an illegal loan during the 1999 race for the leadership of his Likud party (search).

But the charge of a secret connection to Tannenbaum could be the most serious.

The prisoner swap with Hezbollah guerrillas was deeply controversial here, especially among hard-line Israelis who form the core of Sharon's support. The trade — 436 Arab prisoners and the bodies of 59 slain guerrillas for Tannenbaum and the bodies of three Israeli soldiers — was the first time Israel freed prisoners in exchange for an Israeli civilian kidnapped on private business.

Critics said the deal strengthened Hezbollah's standing and would encourage militants to snatch Israeli civilians around the world.

Maariv commentators called Wednesday for Sharon to resign immediately.

"Please put the keys to the state on the table and vacate your position ... not tomorrow, not the day after, not next week. Today, now," reporter Ben Caspit wrote.

The newspaper reported that Sharon's commitment to securing Tannenbaum's release had baffled security officials.

"It is difficult even today to understand what prompted the Prime Minister to fight so hard for him," Maariv quoted a military source as saying.

The newspaper reported that Cohen, father of Tannenbaum's ex-wife, Esther, helped run Sharon's farm in the 1970s and later helped form a company that took over the farm's management in 1977 when Sharon became agriculture minister.

Cohen denied ever telling Sharon about his connection to Tannenbaum.

"For about 30 years, since 1975 I have neither seen him nor spoken to him," Cohen told Israel Radio. He said the missing man's children had asked him, their grandfather, if they could use his name to urge Sharon to make every effort on their father's behalf.

"I told them, 'Don't say that you're my grandchildren, don't even send my regards, so no one thinks you're looking for special favors,'" Cohen said.

Since his release, Tannenbaum admitted he was an indebted gambler lured into a Hezbollah trap by a drug deal. However, some security officials suspect Tannenbaum had actually planned to sell Israeli military secrets.

The Haaretz daily reported Wednesday that before setting out on the October 2000 trip to Dubai, which ended with his detention in Lebanon, he built up an unauthorized stockpile of classified defense documents that investigators suspect may have been intended for sale abroad.