Groping incidents and other harassment targeting female commuters increased on some Tokyo-area train lines last year, despite an increase in women-only cars, according to police officials.

The overall number of reported groping cases in Tokyo dropped slightly in 2005, but authorities are worried by a marked increase of attacks on a number of lines that introduced or increased women-only cars last year, the officials said.

"We've been calling on passengers to prevent such nuisances on trains with announcements and posters, but there were still victims and there were calls" for women-only trains, said JR East spokesman Yuichi Ogasawara.

Anonymous groping of women on crowded trains has long been a social concern.

Passengers during rush hour are often so jam-packed they are immobilized in a crush of bodies and victims have no way of escaping. Offenders can easily disappear into the crowd at the station.

A dozen railways introduced or increased the number of female-only cars last year in hopes of providing some separation of the sexes on crowded lines.

The number of reported cases of groping and other lewd behavior toward women and girls -- including secretly taking photographs -- dropped in Tokyo from a record high 2,201 in 2004 to 2,137 in 2005, a fall of about 3 percent.

Arrests for such crimes were also down, from 1,897 in 2004 to 1,853 in 2005, police said.

But the number of arrests on JR East's Chuo Line as well as Keio Corp.'s Keio Line rose after women-only cars were added. Arrests on the Chuo Line, which introduced female-only cars last September, numbered 217 in 2005, the highest among all lines in the Tokyo area, from 188 in 2004.

On the Keio Line, which first introduced women-only cars in 2001 for late-night riders and extended the service to rush hours last year, there were 146 arrests in 2005, up from 122 the year before.