US-led coalition airstrikes reportedly hit a meeting of high-level Islamic State members near Mosul Thursday, in the latest assault in a months-long campaign to dislodge the extremist group from its bastions in Iraq and Syria.

The US Combined Joint Task Force said in a statement that American and coalition aircraft struck an "ISIL tactical unit and destroyed an ISIL weapons cache" along with a car rigged with explosives near the insurgents' stronghold of Mosul. The Islamic State is also known as ISIL, ISIS or Daesh.

Casualty figures were not immediately known, but Al Arabiya News reported some 15 Islamic State militants were killed in attacks near Mosul in the same time period. The Pentagon told VICE News it could not confirm that the announced strikes were the same as those referenced in media reports. However, a spokesperson for the Combined Joint Task Force, elaborating on the earlier statement, told VICE News that seven strikes were carried out near Mosul on Thursday, destroying "six ISIL buildings and an ISIL fighting position," and striking "three ISIL fighting positions, five ISIL tactical units, two buildings and a large ISIL unit."

Meanwhile, clashes between Islamic State militants and Iraqi security forces near Fallujah Thursday reportedly resulted in the death of Mohanned Salih al-Suwaidi, who is said to be a high level member of the extremist group, according to Al Arabiya.

The bombings followed 29 airstrikes launched in both Syria and Iraq on Wednesday. Planes staged attacks near the besieged Kurdish enclave of Kobani, Syria along the Turkish border, according to the US military, while action in Iraq saw strikes conducted near Mosul, Fallujah and Sinjar.

The stepped-up air campaign came as the UN and a monitoring group announced 2014 was the deadliest year yet in Syria's civil war, and the bloodiest for civilians in Iraq since 2006 and 2007.

The UK-based Syrian Observatory for Human Rights said 76,021 people were killed in Syria last year, half of them civilians.

The UN Assistance Mission in Iraq (UNAMI) reported at least 35,408 civilians were killed or wounded in the same period, although that toll is likely an underestimate given the mission's lack of access to large swaths of the country.

"UNAMI has also received, without being able to verify, reports of significant numbers of casualties along with unknown numbers of persons who have died from secondary effects of violence after having fled their homes due to exposure to the elements, lack of water, food medicines and healthcare," the mission said in a statement.

UNAMI added that 1,101 Iraqis — more than half of them civilians — were killed in acts of terrorism or violence in December, marking the highest death toll in a single month since 2008.

American forces, present in Iraq since June in an advisory capacity, are now reportedly being drawn closer to fighting on the ground. The Washington Post reported Friday that some 300 American troops in Anbar province are caught in the middle of battles between Iraqi security forces, local militias and Islamic State fighters. A base in Anbar where the Americans are headquartered has been hit several times in past weeks.

President Obama has repeatedly assured the public that US forces would not be drawn back into direct confrontation in Iraq. In November, the president announced that the American presence in the country it formerly occupied between 2003-2011 would double to roughly 3,000 troops.

The US has not announced civilian casualty figures resulting from its bombing campaigns in Iraq and Syria. It has also not indicated whether it will pay compensation to the families of those killed — a break from previous policy. In September, Human Rights Watch accused the US of killing at least seven civilians in a series of strikes on Idlib, Syria and urged an investigation into "possible violations of the laws of war."

"When an allegation of civilian casualties caused by US forces is determined to be credible, we investigate it fully and strive to learn from it so as to avoid recurrence," a Combined Joint Task Force spokesperson told VICE News. "That said, we are aware of claims of suspected civilian casualties related to US airstrikes in Syria and Iraq and we continue to evaluate them. To date, we have not been able to verify any of them."