The blog said a directive issued under Hillary Rodham Clinton's name last year ordered American diplomats to seek details about both UN communication systems and personal details for top officials.
Quotes from the more than 250,000 cables obtained by the whistleblowing website WikiLeaks were circulated to the newspaper as well as other media outlets in the US, Germany, France and Spain.
The documents reveal that Saudi Arabia's King Abdullah had "frequently" urged the US to launch an attack against Iran in order to scupper Tehran's nuclear ambition, the Guardian said.
They showed the US has relentlessly pressured other countries, including close allies such as Italy and France, to distance themselves from Iran and assist US efforts to isolate Tehran.
The Guardian planned to publish more revelations on its website ahead of publication in the newspaper Sunday.
These include "claims of inappropriate behaviour" by a British royal and allegations of links between Russia's government and organised crime, the blog said.