Al Qaeda militants now in detention planned to kill Saudi government and security officials and media workers by sending poisoned gifts to their offices, an interior ministry official told Reuters on Saturday.
The group "planned to rob banks and companies to finance their operations", the official, who declined to be named, said.
Last month Saudi Arabia said it captured 149 Al Qaeda militants in recent months who were raising money and recruiting members to carry out attacks inside the kingdom, targeting government facilities, security officials and the media.
"Using poisoned perfume which they planned to send as gifts is one of the ways the arrested people planned to carry out their assassinations," the interior ministry official said.
The militants, who revealed the information to Saudi security forces, belonged to 19 Al Qaeda cells and included 124 Saudis and 25 foreigners. The groups had links to militants in Somalia and Yemen, the interior ministry said last month.
Saudi Arabia has been fighting Al Qaeda militancy for years and quelled a three-year Al Qaeda campaign of violence in 2006. Al Qaeda's Yemeni and Saudi wings merged in 2009 into a new group, Al Qaeda in the Arabian Peninsula (AQAP), based in Yemen.
In August 2009, a suicide bomber posing as a repentant militant tried to assassinate Saudi Arabia's top anti-terrorism official, Prince Mohammed Bin Nayef, but inflicted only minor injuries.
In October, a plot to send two parcel bombs from Yemen to the United States was foiled after a tip off from Saudi Arabia.
"Changes from explosives to chemicals is significant because it demonstrates resolve and the ability to try to trick the security services," said Theodore Karasik, a security analyst at Dubai-based group INEGMA.
"This is a change in tactics. It means they are trying every possible way to spread chaos... The security services are very lucky that they discovered this," he said.
The arrests announced last month were one of the largest Al Qaeda sweeps by Saudi Arabia in years. In March, the kingdom arrested 113 Al Qaeda militants including alleged suicide bombers who it said had been planning attacks on energy facilities in the world's top oil-exporting country.
"We are still investigating the whole thing," the official said.