Saudi King Abdullah suggested implanting electronic chips in detainees from Guantanamo after their release to track them, leaked documents on the US lockup in Cuba indicated Tuesday.

German news weekly Der Spiegel, one of several media outlets to have obtained the documents from the WikiLeaks website, reported in its online edition from a diplomatic cable dated March 22, 2009.

The cable, classified as "secret", recounts a wide-ranging, 90-minute discussion between King Abdullah and US President Barack Obama's anti-terrorism advisor John Brennan in Riyadh on March 15 of that year.

Beyond issues such as Iran, Iraq and the Middle East, they also covered Guantanamo, where a large number of Saudi citizens were detained.

According to the report, Abdullah expressed concern about how to keep tabs on the men if they were to be released, after Obama pledged in January 2009 to close the camp within a year.

"I've just thought of something," the king said, according to the cable.

The cable continues by stating that Abdullah "proposed implanting detainees with an electronic chip containing information about them and allowing their movements to be tracked with Bluetooth".

"This was done with horses and falcons," the king was quoted as saying.

Brennan reportedly replied, "Horses don't have good lawyers," and said that such a proposal would face legal hurdles in the United States.

But he agreed that keeping track of the detainees was an "extremely important issue" and that he would review it with the appropriate officials once he returned to Washington.

Obama has struggled to close the hotly disputed Guantanamo prison and his administration denounced the "unfortunate" release of the classified documents by WikiLeaks.