MOSUL, Iraq (AP) -- Iraq's special forces worked Sunday to clear neighborhoods on the eastern edge of Islamic State-held Mosul as bombings launched by the extremist group elsewhere in the country killed at least 20 people.
The Mosul offensive has slowed in recent days as Iraqi forces have pushed into more densely populated areas, where they cannot rely as much on airstrikes and shelling because of the risk posed to civilians, who have been told to stay in their homes.
"There are a lot of civilians and we are trying to protect them," said Lt. Col. Muhanad al-Timimi. "This is one of the hardest battles that we've faced till now."
Some civilians are fleeing the combat zone, while IS militants are holding others back for use as human shields, making it harder for Iraqi commanders on the ground to get approval for requested U.S.-led coalition air strikes. Iraq's special forces are some of the country's best troops, but they still largely rely on air support to clear terrain.
Iraqi forces first entered the eastern edge of the city on Tuesday. On Friday, forces began pushing into Mosul proper, but so far have advanced just over a kilometer (mile) into the city.
On the southern front, Iraqi forces are still some 12 miles (20 kilometers) from the city center. The fighting is centered on the town of Hamam al-Alil, where Associated Press journalists could hear gunfire and saw attack helicopters firing on IS positions.
Kurdish peshmerga fighters launched mortar rounds and fired heavy artillery at the IS-held town of Bashiqa, about 8 miles (13 kilometers) northeast of Mosul. The town, which is believed to be largely empty except for IS militants, has been encircled by Kurdish forces.
The extremists captured Mosul and surrounding areas in 2014, and have had plenty of time to dig trenches, block off roads and mine approaches to the city.
"Daesh dug trenches that they filled with water and they have a lot of suicide attackers and car bombs," said al-Timimi, using the Arabic acronym for the IS group.
The extremists meanwhile struck far from the front lines with a series of bombings.
The deadliest attack took place in the city of Samarra, 60 miles (95 kilometers) north of Baghdad, which is home to a major Shiite shrine. Provincial spokesman Ali al-Hamdani said the attacker set off a bomb-packed ambulance in a parking lot near Shiite pilgrims before detonating his explosives vest.
The attack killed 11 people, including at least four Iranians, and wounded up to 100 other people.
Another suicide attacker rammed an explosives-laden car into a busy checkpoint outside the city of Tikrit, killing at least nine people. Al-Hamdani said five female students, a woman and three policemen were killed in the attack, while 25 others were wounded.
IS had also captured Tikrit during its lightning blitz across Iraq in the summer of 2014. Iraqi forces drove the militants from the city, around 80 miles (130 kilometers) north of Baghdad, in April 2015.
Iran's Foreign Ministry spokesman, Bahram Ghasemi, condemned the two attacks, which he said had killed 21 people, including 10 Iranian pilgrims, the semi-official Mehr news agency reported. It was not immediately possible to reconcile the conflicting tolls, which are common in the chaotic aftermath of attacks.
In an online statement, IS claimed all three bombings and said the ambulance bomb was set off by a second suicide attacker. The AP could not verify the authenticity of the statement, which was posted on a militant website commonly used by the extremists.
In the capital, Baghdad, a series of smaller bombings killed at least 10 people and wounded 21 others, according to police and medical officials, who spoke on condition of anonymity because they were not authorized to brief reporters. No one immediately claimed the attacks, but they bore the hallmarks of IS.