OSAKA — Nissin Food Products Co., a leading food maker based in Osaka, received an extortion letter Wednesday containing a threat to put needles in its products unless the company pays 5 million yen, police sources said Saturday.

The incident comes shortly after another Osaka-based company, Santen Pharmaceutical Co., was the target of a similar extortion attempt. The letter sent to Santen demanding money also arrived on Wednesday.

The sources said, however, they do not believe the two cases are related because of a difference in writing style in the letters and the fact they carried different postmarks.

The Nissin extortionist, identified only as the “Lupin Group,” sent the letter to President Koki Ando, specifying the time and place for the company to deliver the money, the sources said.

A spokesman for Nissin said he would not comment on details of the case because the company is leaving the matter to police.

He said the firm is not planning to withdraw its products from shops because there has been no further contact from the extortionist and no tampered products have been reported so far.

Nissin Food has frequently been the target of similar extortion attempts in recent years. Last year, three people were arrested on suspicion of attempting to extort money from the firm.

Earlier this month, an employee of an Internet home page production company was arrested after he allegedly sent an extortion e-mail to the firm demanding 40 million yen.

Threats against Santen

Meanwhile, police suspect the extortion attempt against Santen was “a vicious prank,” the sources said.

The drugmaker started Thursday to remove all its eyedrop products from shop shelves, one day after it received the letter along with a bottle of Santen eyedrops which police said contained benzene.

The extortionist, who demanded 20 million yen from the company, has not re-established contact since mailing the letter, the sources said. The letter did not make any suggestions as to why the extortionist was targeting the firm or whether the sender holds a grudge against the company.

The letter, which also carried an Osaka postmark, specified the time and place for Santen to deliver the extortion money, but no one turned up at the site at the prescribed time, according to the sources.

Another element that has led police to believe the case was a prank is that the letter did not warn Santen against telling police about the extortion attempt, a practice common among blackmailers, police sources said.

The extortionist threatened in the letter to randomly contaminate Santen eyedrop products with the solvent toluene.

The letter, sent to Santen’s headquarters, demanded that the company deliver the cash to a location in Osaka on Thursday morning and post an advertisement in a newspaper as a sign that it agreed to the terms, the sources said.

The letter said the extortionist would phone the company to give directions on how the cash should be handed over, but he subsequently failed to do so, they said.