RIYADH, Nov 7 (Reuters) - Saudi Arabia's religious leaders accused Muslim militants in the kingdom on Friday of violating the teachings of Islam and threatening its most sacred sites.

After two separate clashes between gunmen and security forces in the holy city of Mecca, the preacher at Mecca's Grand Mosque said the militants were trying "to destabilise the security of these safe places".

"They have violated the sanctities of time and place and committed terrorism, violence, bombings, crime and corruption," Sheikh Abdulrahman al-Sudeis told worshippers in a sermon at Friday's noon prayers.

Saudi Arabia said two Muslim militants blew themselves up on Thursday during a police raid in Mecca, part of the country's crackdown on suspected al Qaeda activists following suicide bombings which killed 35 people in the capital, Riyadh, in May.

The raid came three days after two other militants, believed to be linked to Saudi-born Osama bin Laden's al Qaeda network, were killed in a shootout with security forces. Another was shot in a dawn clash with police in Riyadh on Thursday.

Last week the United States and Britain warned of possible terror attacks in Saudi Arabia during the Muslim fasting month of Ramadan, which runs until late November. Sudeis told worshippers Ramadan should be a time of forgiveness and mercy.

The kingdom's top religious official, Grand Mufti Sheikh Abdulaziz bin Abdullah al-Sheikh, condemned the two men who died in Mecca, saying they had violated Islamic teachings by attempting to attack "the house of God" and then by fleeing from security forces and killing themselves.

"All these are forbidden (in Islam)," he told the Saudi newspaper al-Jazirah.

Sudeis stressed the need to teach Saudi youth moderation.

Riyadh, trying to quash militancy and improve its image abroad, has fired hundreds of clerics for inciting dissent.