In a statement delivered by the head of court on Friday, King Hamad bin Isa al-Khalifa said: "with all due respect to foreign experts", only moderate Bahrainis were welcome to comment on the kingdom's internal affairs.
"It is a national duty that citizens take a responsible attitude when it comes to exercising their right to free speech."
The statement, carried by the official Bahrain News Agency, said a reform process launched in 2002 was "gradually bearing fruit."
Four opposition parties, which boycotted legislative polls in 2002, have said they are pressing ahead with plans to hold a conference on Bahrain's "constitutional crisis", although the government said they needed prior authorisation.
Organisers of the conference due to start on Saturday have said they have invited foreign and Arab legislators to attend.
Points of issue
The parties are mainly opposed to the equal legislative powers accorded to the appointed Majlis al-Shura consultative council, which like its elected counterpart has 40 members.
Bahrain's elected parliament was revived in 2002 as part of reforms which turned the Gulf state into a constitutional monarchy.
It was dissolved in 1975 after it clashed with the government over a state security law.
In the shadow of the Iraq conflict and the tussle over reforms in neighbouring Saudi Arabia, the kingdom has made limited progress in reform and democratisation.
"The security situation has calmed down but the political one is still in a stalemate," Shaikh Ali Sulayman, chairman of the Shia popular mainstream al-Wifaq Society.
Although Shia are represented, representation is not proportional to their numbers.
However, human rights have greatly improved as government and opposition alike adhere to peaceful political means.