BAGHDAD — Iraq’s special forces declared their aspect of the mission to reclaim Mosul completed Saturday.

However, heavy fighting still looms between other Iraqi forces and the Islamic State as it clings to a dwindling portion of Iraq’s second largest city.

The Islamic State still controls part of western Mosul, including the dense Old City, where some of the toughest battles are expected to play out. It remains to be seen which of the government forces encircling Mosul will be tasked with assaulting the final stronghold districts.

Special forces spokesman Sabah al-Numan said his troops had finished retaking the area assigned to them, but stood ready “to support any other forces if we are ordered to by the prime minister.”

Elsewhere in central and southern Iraq, a series of bombings killed at least 27 people.

A suicide bombing near the oil-rich city of Basra killed at least eight people and wounded 41 others, according to a military commander.

Five civilians and three troops were killed when the bomber blew up his explosives-laden car Friday at a checkpoint north of Basra just behind a bus waiting to be cleared, said chief of the Basra Operations Command, Lt. Gen. Jamil al-Shimmari.

A second attacker drove down a desert road after the explosion and security forces killed him, al-Shimmari said.

In an online statement, the Islamic State claimed responsibility for the attack, saying it targeted Shiites.

Basra, about 340 miles southeast of Baghdad, is home to about 70 percent of the country’s proven oil reserves of 153.1 billion barrels. Located on the Persian Gulf and bordering Kuwait and Iran, the city is also Iraq’s only outlet to the sea and the hub for most of the country’s oil exports, with 3.23 million barrels exported from Basra last month.

The Islamic State also claimed responsibility for double suicide bombings in Baghdad overnight that killed at least 19 people and wounded 33, according to an online statement.

Iraqi forces, backed by the U.S.-led coalition, officially launched the operation to retake Mosul in October and the city’s east was declared “fully liberated” in January. The fight for Mosul’s west was launched the next month and has been marked by some of the most grueling and deadly combat in the fight against the Islamic State in Iraq to date.