US forces who bombed Islamic State in Iraq and the Levant (ISIL) fighters in Syria also targeted a separate armed group plotting an imminent attack against US and Western forces, the US defence ministry has said.

Arab allies Bahrain, Jordan, Saudi Arabia, Qatar and the United Arab Emirates took part in the strikes, which started early on Tuesday, it added.

Eight US airstrikes were aimed at the Khorasan group which is made up of experienced al-Qaeda operatives, the Pentagon said in a statement.

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"The United States has also taken action to disrupt the imminent attack plotting against the United States and Western interests conducted by a network of seasoned al-Qaeda veterans - sometimes referred to as the Khorasan Group - who have established a safe haven in Syria to develop external attacks, construct and test improvised explosive devices and recruit Westerners to conduct operations," the statement said.

The US military used fighter jets as well as remotely piloted aircraft and Tomahawk missiles to conduct 14 strikes against ISIL.

"The strikes destroyed or damaged multiple ISIL targets... and included ISIL fighters, training compounds, headquarters and command and control facilities, storage facilities, a finance center, supply trucks and armed vehicles," the statement said.

A total of 47 Tomahawk missiles were fired by US ships in the Red Sea and and the North Arabian Gulf.

The Khorasan group that was targeted separately is linked to the Al-Nusra Front, which is the Syrian affiliate of al-Qaeda.

Tens of ISIL fighters were killed or wounded in the strikes on the ISIL stronghold of Raqqa and surrounding areas, according to the Syrian Observatory for Human Rights, which gathers information from a network of activists on the ground.

More than 20 members of ISIL were killed in strikes on two of the organisation's positions in Raqqa province. The strikes completely destroyed the two positions as well as vehicles stationed there, the monitoring group said.

The US airstrikes against positions of al-Qaeda's Syria affiliate Al-Nusra Front killed at least 50 fighters, the observatory said, adding that multiple attacks targeted an area in western Aleppo province.

At least 120 fighters have been killed in Syria on Tuesday, including more than 70 members of ISIL and 50 al-Qaeda fighters, according to the observatory. Eight civilians were killed by US strikes in Aleppo province.

Damascus 'notified'

The Syrian government said it had received a letter from US Secretary of State John Kerry delivered by the Iraqi foreign minister telling it that the US and its allies planned to attack ISIL in Syria.

Russia criticised the airstrikes, saying a one-sided 'notification' to the Syrian government was not enough, adding that the strikes would fuel tension in the region.

"Any such action can be carried out only in accordance with international law," the Russian foreign ministry said in a statement. "That implies not a formal, one-sided 'notification' of airstrikes but the presence of explicit consent from the government of Syria or the approval of a corresponding UN Security Council decision."

The US military said its partners in airstrikes included Jordan, Bahrain, Saudi Arabia, Qatar and the United Arab Emirates. 

Jordan's minister of information and communication, Mohamamd Al Momani, confirmed that his country participated in the strikes. Momani said the airstrikes would continue in the coming period.

The minister said Jordan participated to strike "terrorism in its home in order to protect Jordan's security and stability and to prevent terrorism from reaching the kingdom".

The attacks come just two weeks after the US formed a coalition to confront the ISIL group, which has taken over large areas of Syria and Iraq and declared a "caliphate".

Syrian Kurds urged US airstrikes against ISIL

The coalition includes Nato, non-members including Australia and Arab nations.

The US president, Barack Obama, said on September 10 that an expanded campaign would degrade and ultimately destroy the group.

The attacks also come a day after ISIL's spokesman, Abu Mohammed al-Adnani, called on supporters of the group to attack foreigners wherever they are.

In a 43-minute video, Adnani said: "If you can kill a disbelieving American or European - especially the spiteful and filthy French - or an Australian, or a Canadian, or any other disbeliever from the disbelievers waging war, including the citizens of the countries that joined a coalition against the Islamic State, then rely upon God, and kill him in any manner.''

Al Jazeera's Imran Khan, reporting from Baghdad, said the timing of the coalition's attacks must have been seen in the context of ISIL's announcement.

"This was a doctrinal shift by ISIL, previously they maintained they weren't at war with the US and its allies and that their key goal was to strengthen the caliphate."

ISIL released another video on Tuesday that appears to show British journalist John Cantlie criticising preparations for US-led attacks on the group, the SITE monitoring service reported.

The video appeared to have been recorded before the US-led airstrikes overnight in Syria.

Source: Al Jazeera and agencies