The US Treasury added Saudi-born Abd al-Rahman Muhammad Zafir al-Dubaysi al-Juhni and Iraq native Abd al-Rahman Mustafa al-Qaduli to its list of Specially Designated Global Terrorists on Wednesday.

The two were cited for their ties to, respectively, al-Qaeda operations in Syria, and al-Qaeda breakaway group the Islamic State of Iraq and the Levant (ISIL).

Al-Juhni is part of a group of senior Qaeda operatives in Syria formed to attack Western targets outside the country and also to mediate tensions between ISIL and the al-Nusra Front, the local Qaeda affiliate, the Treasury said.

Al-Qaduli is a senior ISIL official who joined Qaeda 10 years ago and previously worked for leader Abu Musab al-Zarqawi, formerly the Qaeda commander in Iraq, it said.

The designation aims to limit their access to financial and business networks by banning any American or American business from dealings with them and freezing any US assets.

Treasury Under Secretary for Terrorism and Financial Intelligence David Cohen said the act sends a message to other Syrian militants to not work with them.

"We are very concerned about al-Qaeda networks moving money and fighters to extremist groups in Syria," he said in a statement.

The action "sends a strong warning to the legitimate Syrian opposition and those who wish to support it that they must reject the attempts of al-Qaeda, ISIL, and al-Nusra to elicit support for their cause by preying on the sympathies of the international community for the plight of the Syrian people."

Syria sank into war in March 2011 when pro-reform protests turned into a massive insurgency following the intervention of Western and regional states.

The unrest, which took in terrorist groups from across Europe, the Middle East and North Africa, has transpired as one of the bloodiest conflicts in recent history.

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