Chanting secularist slogans and waving Turkish flags, more than 300,000 people from all over Turkey rallied Saturday to discourage Prime Minister Recep Tayyip Erdogan, a conservative with an Islamist political past, from running for the presidency.

The demonstrators marched to the mausoleum of Mustafa Kemal Ataturk, the founder of modern secular Turkey in 1923, transforming the normally hushed venue into an unprecedented demonstration ground.

“Turkey is secular, it will remain secular”, “The presidency’s roads are closed to Sharia (Islamic law)”, “An imam cannot become a president”, they chanted, reflecting concerns that Erdogan and his Justice and Devlopment Party (AKP) are not truly committed to the mainly Muslim nation’s secular system.

Stay tuned.

UPDATE: InstaPundit’s correspondent in Turkey, Claire Berlinski, emails:

I wasn’t there, but it was definitely a state-run (i.e., nationalist, Kemalist) show. This was planned a long time ago. It doesn’t necessarily mean much about what people are really thinking. By the way, the fact that Turkish nationalists are anti-Islamists should not lead anyone to conclude that they’re Western-style democrats. Despite ErdoÄŸan’s Islamist past, one of the basic conflicts here is that he wants to open Turkish society. Here’s a good discussion of this point. The demonstrators are concerned that ErdoÄŸan isn’t committed to secularism, probably for good reason, but ErdoÄŸan’s supporters are — also for good reason — concerned that the Kemalists’ aren’t committed to democracy.