The head of Saudi Arabia's religious police has warned citizens against using Twitter, which is rising in popularity among Saudis.
Sheikh Abdul Latif Abdul Aziz al-Sheikh said anyone using social media sites - and especially Twitter - "has lost this world and his afterlife".
Twitter was the platform for those who did not have any platform, he said.
His remarks reflect Riyadh's concern that Saudis use Twitter to discuss sensitive political and other issues.
The conservative kingdom is believed to have seen the world's fastest increase in the uptake of Twitter, says the BBC's Sebastian Usher.
The sheikh's comments echo those of the imam of the Grand Mosque in Mecca in April who used his sermon - seen by millions on TV - to warn that Twitter was a threat to national unity, our correspondent says.
Earlier, Saudi Arabia's grand mufti, the kingdom's most senior Muslim cleric, had dismissed Twitter users as "fools".
These rhetorical attacks are part of a concerted offensive by the Saudi establishment on the social network site, our correspondent says.
Many Saudis have seized on Twitter as the most immediate and effective way to open little windows into a traditionally opaque society.
Recent protests in the Eastern Province have been tweeted and images of human rights activists on trial have been uploaded directly from courtrooms, challenging many taboos.
In response, the authorities have mooted moves that could inhibit Twitter users by linking their online accounts to their Saudi ID numbers.
A number of web activists have been detained, including at least one for the alleged apostasy, a charge that could carry the death penalty.
However, some elements of the Saudi elite have also warned against moving too hard on social network users.
Billionaire businessman Prince Alwaleed Bin Talal, who presents himself as a reformist, has described attempts to restrict social media as a losing battle.