A fourth official in western Austria has opened a package containing acid, but was not injured, authorities said Saturday as they widened their investigation into the mysterious targeting of politicians in the area.

Alois Lissl, director of public safety in the province of Upper Austria, told reporters the latest acid package -- mailed like the others from neighboring Germany -- was delivered late Friday to an unidentified administrator in the town of Raab.

The administrator opened the package but was not injured by the corrosive liquid it contained, Lissl said.

On Friday, an official in the town of Weisskirchen was treated at a hospital for burns to a hand and foot after he opened a package at his home office. Police said they intercepted two other similar packages sent to other officials in the town about 200 kilometers (120 miles) west of Vienna.

All four packages were mailed from Passau, Germany, just over the border from the western Austrian city of Linz, Lissl said Saturday.

Federal counterterrorism officials took charge of the investigation, Austrian media reported Saturday, and experts with the Federal Criminal Investigations Bureau -- Austria's equivalent of the FBI -- were examining the packages for clues.

Results from forensics tests being conducted in Salzburg were not expected until sometime next week.

Investigators said they still could not be certain the same individual sent all four packages, though police said they were working on the assumption that whoever mailed them held a grudge.

Officials said the exact motive remained unclear, since the official who suffered the burns -- former Weisskirchen mayor Rudolf Prinz -- is a member of the ruling Social Democratic Party, yet two of the other packages targeted officials with the conservative Austrian People's Party.

Police were interviewing the officials' neighbors Saturday to determine whether any of them had signed for suspicious packages or could offer any other information, Lissl said.

Prinz, 61, said he was injured when he opened the book-sized package and it released a noxious vapor. In addition to the burns on his hand and foot, he was treated for inflammation to his nasal passages.

"It burned my eyes, my nose and my skin, and it stank up the whole house," Prinz told Austrian public broadcaster ORF.

Josef Puehringer, the governor of Upper Austria province, condemned what he called "this underhand act" and demanded those responsible be brought to justice.

Austria's Interior Ministry cautioned local officials against opening any packages or letters that might seem suspicious and warned the public of the possibility of copycat incidents in coming days.