A 50-year-old man has been arrested on charges of spreading a rumor online that a South Korea-U.S. military drill was responsible for last month's deadly ferry sinking off South Korea's southwest coast, police said Wednesday.

The suspect, identified only by his family name Shin, disseminated the rumor that "the ferry Sewol sank because it deviated from its course due to the joint South Korea-U.S. exercise," according to the National Police Agency.

Shin posted the claim on an online bulletin board of a portal site, three days after the ferry sank on April 16 and left more than 300 people dead or missing.

Shin also cited warnings of a joint shooting exercise issued for certain areas in the Yellow Sea by the oceanographic administration for April 15-16 to back up his claim. The navigation warnings "show why the ferry Sewol went off the planned course and used a difference route where the accident took place," Shin argued in the posting.

Rejecting Shin's claim, the police said that the joint shooting drill took place only on April 15 but that Shin doctored the image of the data to show that the shooting exercise was also conducted on April 16.

Shin also uploaded the photograph of a U.S. nuclear-powered submarine operating in the Yellow Sea off the west coast, claiming the ill-fated ferry was trying to circumvent the military vessel, but the police rejected the claim, saying that the photo was taken randomly from the Internet.

The police opened an investigation into the posting after the Navy filed a complaint over the Internet rumor late last month.

The 6,825-ton ferry capsized and sank in waters off South Korea's southwestern island of Jindo last month. The death toll reached 268 as of Wednesday, with 34 people still believed to be trapped in the ferry. (Yonhap)