The Iraqi army has reached the centre of the northern city of Beiji, as they continue their effort to break the siege of the Islamic State of Iraq and the Levant (ISIL) on the country's biggest oil refinery nearby.

Exclusive images obtained by Al Jazeera on Monday showed government forces pushing ahead into the rebel-controlled city, with ISIL's flag covered with an Iraqi security forces slogan.

Al Jazeera's Imran Khan, reporting from Baghdad, said clashes continue and the armed rebels are fighting back.

He said the oil refinery, located about 50km from the city centre, is the next big target. ISIL fighters remain in control of parts of the facility.

The military advance is seen as a significant victory for the government, as Beiji and its nearby oil refinery were one of the first territories swept by ISIL in June.

On Sunday, Iraqi troops entered Beiji, a city of about 200,000 people, from the south and west and took over the al-Tamim neighbourhood and city centre.

ISIL placed bombs along roads and deployed snipers to keep government forces from advancing, tactics used in other cities held by the Sunni armed group, which controls swathes of both Iraq and Syria.

In an exclusive interview with Al Jazeera, Ahmed Adb al-Joubouri, minister of state for provincial affairs, urged Iraqi men to join the fight in Beiji and elsewhere.

"If we don’t act now then ISIL will sweep us so we have to give big support to the youth to join the fight against ISIL especially in Salahhuddin province as it is considered the breaking point for ISIL’s advance towards Baghdad," he said.

Meanwhile, Beiji resident Sultan al-Janabi told Reuters by telephone from his house that clashes had been raging since the advance.

Baghdadi's fate unclear

In a related development Major Curtis Kellogg, a spokesman at the US military's Central Command, said it had no information to corroborate media reports that ISIL leader Abu Bakr al-Baghdadi was wounded in a strike on the city of Mosul in the north and al-Qaim to the west.

"We cannot confirm that Baghdadi was present when we struck the convoy near Mosul on Friday night," he said.

A Twitter account claimed Baghdadi had been wounded by a US strike, but other accounts that support ISIL said the report was untrue.

Al Jazeera is trying to verify the authenticity of the Twitter account.

A member of western Anbar Province's security committee said he had heard unconfirmed reports that Baghdadi had been wounded and moved to Syria.

Several other Anbar officials gave contradictory reports on Baghdadi's fate.

On Friday, the United States, which fought ISIL's predecessor al-Qaeda during the American occupation of Iraq, said it will send up to 1,500 more troops to train Iraqi forces. Britain also plans to send trainers.

US air strikes, launched after ISIL beheaded Western hostages, have slowed down the group and enabled Iraqi security forces to make some gains.

Source: Al Jazeera and agencies