Iraqi forces are "ahead of schedule", the Pentagon says, as they begin the second day of the battle to retake Mosul from so-called IS fighters.

But Pentagon spokesman Peter Cook warned it "could take some time" as it remained to be seen whether Islamic State (IS) would "stand and fight".

Fighting continued overnight, with IS militants attacking Iraqi army tanks.

A BBC correspondent with government forces says the current front line is 20km (12 miles) south of the city.

IS seized Mosul, then Iraq's second-largest city, in June 2014.

The extremists' leader Abu Bakr al-Baghdadi then chose Mosul as the place to announce the forming of a caliphate, so retaking the city would be "symbolic", according to Mr Cook.

Mr Cook told reporters in Washington: "Early indications are that Iraqi forces have met their objectives so far, and that they are ahead of schedule for this first day. This is going according to the Iraqi plan - but again, it's early, and the enemy gets a vote here. We will see whether ISIL [IS] stands and fights.

"We are confident no matter what, however, that the Iraqis have the capabilities to get this job done, and we stand ready to support them, along with the rest of the coalition."

A coalition of 30,000 Iraqi and Kurdish Peshmerga forces and Sunni tribal fighters began their advance on lS's last major stronghold in the country after months of planning on Monday.

It is thought between 4,000 and 8,000 IS fighters remain in Mosul.

The Kurds seized several villages in the first few hours of the operation, and announced on Monday evening they had achieved all their key objectives, including recapturing 200 sq km and nine villages in under 24 hours.

They also secured an additional significant stretch of the Irbil-Mosul road.

One Kurdish general told the BBC's Orla Guerin: "We have a powerful enemy, They are not just fighting the Kurds or the Shia, they are fighting the whole world.

"We want to defeat them for everyone's sake."

A suicide bomber struck a funeral gathering in Baghdad on Saturday, killing at least 35 people and wounding more than 60, Iraqi police and hospital officials said.

The attack in the Shaab neighborhood occurred around lunchtime, the officials said, speaking on condition of anonymity because they were not authorized to brief the media. The Islamic State group claimed responsibility in a statement carried by its Aamaq news agency.

Hussein Khazem, the owner of a nearby clothing warehouse, said the bomber detonated his payload inside a funeral tent, causing a big explosion.

He saw a large number of killed and wounded people, many burning cars and major damage to the local market. The dead included elderly people, children, and some women. He said he closed his shop to help evacuate the wounded and remove the bodies.

"The security situation is not good at all," he said. "These big incidents are happening again, especially in the poorer residential neighborhoods."

Iraq has seen several bombings in recent months, though most have had lower death tolls than Saturday's attack. In July, a massive car bomb in central Baghdad's popular shopping district of Karradah killed about 300 people and forced the resignation of the interior minister.

The U.S. State Department condemned Saturday's "barbaric" attack, calling it yet another sign of the IS group's "cowardice and contempt for human life and their attempt to sow sectarian discord among the people of Iraq."

Saturday's attack comes as Iraqi security forces are preparing for an operation to retake the militant-held northern city of Mosul, the country's second largest, from IS.

"All the troops are ready, now they are just waiting for the order from the prime minister," said Maj. Gen. Najim al-Jobori, the head of Nineveh operations command and one of the top Iraqi generals overseeing the Mosul operation.

"The head of the snake is Mosul," he said. "I think ISIS knows this is the end of ISIS in Iraq," he added, referring to IS by another acronym.

A Navy ship that came under fire from two missiles launched from rebel-held land in Yemen while it transited through international waters Sunday responded in self-defense with three missiles, a Defense Department official confirmed to Military.com.

USNI news first reported that the Arleigh Burke-class destroyer USS Mason launched a RIM-162 Evolved SeaSparrow Missile and two Standard Missile-2s from the waters of the Red Sea, north of the Strait of Bab-el-Mandeb where it was operating when it came under attack.

A defense official confirmed that the missiles had been launched and also confirmed the outlet's report that the ship had used a Nulka missile decoy, designed to be launched to lure enemy missiles away from their targets.

The Raytheon-made SeaSparrow is designed to intercept supersonic anti-ship missiles, while the SM-2, also made by Raytheon, is the Navy's primary surface-to-air weapon and a key element of shipboard defense for destroyers.

The Mason was responding to two ballistic missiles that originated around 7 p.m. Sunday from Yemeni territory held by Shiite Houthi rebels. The Mason was not hit by the missiles, and an official from U.S. Navy Forces Central Command said Monday it remained unclear if the ship had been specifically targeted.

Previously, a defense official told the Associated Press that the Mason had used onboard defensive measures to protect itself after the first of the two missiles was fired, but until now no one had publicly confirmed that the ship did indeed fire back.

This exchange comes only a week after the high-speed logistics vessel Swift, a United Arab Emirates-leased ship formerly in service for the Navy's Military Sealift Command, was badly damaged by a missile while operating near the Bab-el-Mandeb Strait on Oct. 1. The Saudi-led coalition carrying out airstrikes on the rebels in Yemen said the Swift had been attacked by the Houthis.

UAE officials said the ship was transporting humanitarian aid when it was hit.

Today, the Mason remains in the general area that the exchange took place and is continuing a routine patrol, a defense official told Military.com.