Iraqi security forces have launched an operation to retake the last Islamic State (IS) militant group stronghold in Mosul, the country's second-largest city.
Brett McGurk, the U.S. envoy to the international coalition fighting IS militants, said on Twitter that Iraqi forces breached Mosul's Old City early June 18.
Lieutenant General Abdul-Amir Rasheed Yarallah, who commands army operations in Ninevah Governorate, said Iraqi special forces, the regular army, and federal police were taking part in the operation.
"The initial air strikes started at around midnight. The security forces started storming parts of the Old City at dawn," an officer with Nineveh operations command said.
"This is the final chapter" in the offensive to take Mosul, said Lieutenant General Abdul Ghani al-Assadi, commander of the elite Counterterrorism Service (CTS) units spearheading the assault.
The IS group overran Mosul in 2014, declaring a self-styled "caliphate" over areas it ruled.
Mosul's Old City is a densely populated maze of narrow alleyways where fighting is often conducted house by house.
About 100,000 civilians remain trapped there in harrowing conditions, with little food, water, and medicine and limited access to hospitals, according to the United Nations.
"This will be a terrifying time for around 100,000 people still trapped in Mosul's Old City ... now at risk of getting caught up in the fierce street fighting to come," the International Rescue Committee (IRC) said in a statement.
Iraqi forces backed by the air strikes of the U.S.-led coalition have been pressing a months-long offensive to retake the Old City on the west side of the city from IS fighters.
Taking back the Old City is crucial to recapturing the whole of the former IS bastion.
Thousands of civilians are believed to be trapped in the Old City, where the militants are using them as human shields, UN humanitarian coordinator Lise Grande said June 16. She said conditions are "desperate," with little food and no clean water.
Iraqi forces launched the Mosul offensive in October, retaking the eastern part of the city in January and starting the operation for its western part the next month.
The move on Mosul's Old City comes just one day after the Iraqi military said its forces and Sunni tribal fighters had driven IS extremists out of the Al-Waleed border crossing near Syria, nearly three years to the day after the town fell to IS.
The military statement on June 17 said U.S. and Iraqi aircraft supported ground troops in the offensive on the western edge of Iraq.
Al-Waleed is across from the Syrian border town of Al-Tanf, site of a U.S. base used to aid forces fighting IS and the government and allies of President Bashar al-Assad in Syria’s six-year civil war.
IS took Al-Waleed on June 22, 2014, as its forces captured large chunks of territory from Syrian and Iraqi government forces, declaring capitals in the Syrian town of Raqqa and the Iraqi city of Mosul.
When Al-Waleed fell to IS, it gave the group control of the Iraq-Syria frontier. At the time, they vowed to eliminate the border and establish a "caliphate" over territory in the two Arab nations.
U.S.-backed fighters in both countries are now pressuring IS forces and are attempting to push their final fighters out of the two self-declared capitals.
Along with supporting Iraqi government forces, the United States backs Syrian and Kurdish rebels fighting Assad’s government in Damascus. Russia and Iran have backed Assad.
The presence of the U.S. forces on the Syrian side near Al-Tanf has prevented Iran-backed Shi’ite forces supporting Assad’s government from receiving supplies along the main Baghdad-Damascus highway. The capture of Al-Waleed is likely to aid the U.S. efforts there.
On June 6, the U.S.-led coalition said it had eliminated a unit of Iranian-backed forces fighting on behalf of Assad as it neared the Al-Tanaf base. Russia denounced that attack as an "act of aggression."
The Pentagon on June 14 announced the deployment of the truck-mounted High Mobility Artillery Rocket System (HIMARS) to the Al-Tanf base, also drawing protests from Russia.
Around Raqqa, U.S.-backed Syrian Democratic Forces have seized territory to the north, east, and west of the city as they prepare for the final assault on the IS stronghold.