HIT, Iraq — Heavy resistance has slowed Iraqi forces Tuesday as they pushed forward toward the center of a town held by Islamic State militants in western Anbar province, commanders at the scene said. Hundreds of roadside bombs, car bombs and heavy mortar fire slowed advancing Iraqi troops to a near halt Tuesday after entering the small town of Hit the previous day. Hit — which lies along the Euphrates River in a valley in Anbar’s sprawling desert — is strategically important as it sits along an IS supply line that links territory controlled by the extremist Sunni group in Iraq and in Syria.