NEAR FALLUJAH, Iraq: Iraqi forces stalled at the fringes of Fallujah, slowed in their advance on Wednesday by concerns over the fate of trapped civilians and resistance from the Islamic State group. Fighting also raged hundreds of kilometers (miles) further up the Euphrates Valley in Syria, as US-backed Kurdish and Arab fighters opened a new front against the jihadists in the strategic Manbij pocket on the Turkish border. After a week of shaping operations aimed at sealing the siege of Fallujah, which lies just 50 kilometers (30 miles) west of Baghdad, elite forces launched a new, more aggressive phase on Monday morning. But they have so far been unable to reach the city center and battle IS fighters in the streets of one of their historical strongholds. Prime Minister Haider al-Abadi said concern for the estimated 50,000 civilians the United Nations has said IS was using as human shields was slowing progress.