Iraqi forces have retaken around 30 percent of west Mosul from Islamic State militants, a commander of the elite Counter Terrorism Service said on Sunday, as soldiers pushed into more districts.
Federal police and Rapid Response units said they had entered the Bab al-Tob area of the Old City, where the fight is expected to be toughest due to narrow alleyways through which armored vehicles cannot pass.
The militants are vastly outnumbered and outgunned by Iraqi forces backed by a U.S.-led coalition and are defending their last major stronghold in Iraq using suicide car bombs, snipers and mortars.
As many as 600,000 civilians are trapped with the militants inside the city which Iraqi forces have effectively sealed off from the rest of the territory that Islamic State controls in Syria and Iraq.
CTS troops stormed the al-Jadida and al-Aghawat districts on Sunday, Major General Maan al-Saadi told reporters in Mosul, saying the militants were showing signs of weakness despite initial "fierce" resistance.
"The enemy has lost its fighting power and its resolve has weakened. It has begun to lose command and control," he said, adding that around 17 out of 40 western districts had been retaken.
Saadi said he expected it would take less time to recapture the western half of the city than the east, which was cleared in January after 100 days of fighting.
It is three weeks since Iraqi forces launched a campaign to recapture districts west of the Tigris River that bisects Mosul.
More than 65,000 people have been displaced by the fighting in the past two weeks alone, bringing the total number to more than 200,000 since the campaign to recapture Mosul began, according to the International Organisation for Migration.
In the Mansour district from which Islamic State was driven several days ago, residents collected aid brought by volunteers from east Mosul while helicopters circled overhead, firing heavy machine guns and missiles at targets in the city.
It is by far the largest city Islamic State has held since the group's leader Abu Bakr al-Baghdadi proclaimed a caliphate spanning Iraq and Syria from a mosque in Mosul in the summer of 2014.
The group has been losing ground in both countries to an array of forces, some of which are backed by the United States, others by Turkey, Russia and Iran.
Losing Mosul would be a major blow to Islamic State, but the group is expected to pose a continuing threat, reverting to insurgent tactics such as bombings.
(Writing by Ahmed Rasheed and Isabel Coles; Editing by Robin Pomeroy)