UNESCO expressed Saturday its deep concern over Islamic State's (IS) progression towards the ancient city of Palmyra in central Syria, Middle East News Agency (MENA) reported. "We are very concerned and we are following the situation carefully, as a result of the great value of this archaeological site," the Director-General of the organization, Irina Bokova said in a statement reported by Al Arabiya TV channel "Erasing our collective memory is not acceptable and the protection of our heritage and culture is our response to extremists. Our responsibility is to alert the UN Security Council, in order to take several strong decisions that will prevent this extremism," Bokova added. Since Wednesday, violent clashes have been taking place between IS militants and the Syrian regime's forces in Palmyra, Homs province.