The number of illegal immigrants who die trying to cross into Arizona from Mexico is rising despite tighter border security that was to serve as a deterrent, a border medical examiner says.

Instead, deaths along much of the Arizona border — the busiest illegal entry point on the 1,950-mile U.S.-Mexico frontier — are ahead of the record pace set two years ago, said Dr. Bruce Parks, a medical examiner whose office performs autopsies on many of the illegal immigrants who die in Arizona.

Parks said 181 bodies or sets of remains were recovered between Jan. 1 and Sept 8, compared with 148 in the same period last year. In 2005, officials found 166 bodies during that period.

Many of those victims will have died because of the heat, which regularly exceeds 100 degrees during the hottest part of the Arizona summer.

"We still anticipate finding remains between now and the first of the month," said the Rev. Robin Hoover, founder of the Tucson-based Humane Borders group, which has had search parties out looking for bodies the last two weekends. "There's bodies out there that we know of that we just haven't found yet."

Hoover's group also places water tanks throughout the desert for use by migrants trying to cross the desert from Mexico into the U.S. "Someone will walk out and say 'these two people died' and tell us about where and we go out and try to find them," Hoover said.

Border Patrol statistics show a higher death toll, but the agency's count for 2007 began with the start of the federal fiscal year on Oct. 1. According to federal figures, 197 bodies or remains have been recovered in Arizona's deserts through Aug. 31. In the year-earlier period, 200 were found.

"The patrol doesn't want to see any deaths," said Dove Haber, a spokeswoman in the patrol's Tucson sector, which covers most of the Arizona border except for an area around Yuma. "Our ideal would be that there would be none. The positive is that our rescue numbers are high."

Lloyd Easterling, a Border Patrol spokesman in Washington, said he believes more skeletal remains are being found because the agency's ramp-up of personnel and resources has more agents out patrolling remote, treacherous terrain.

Hoover said the Border Patrol's efforts to shut off migration have just forced illegal immigrants to cross even more dangerous ground.

Easterling said the number of deaths across the entire Southwestern border of the United States stood at 371 as of the end of August, compared to 442 two years ago. The total for all of the 2005 fiscal year was a record 494.