PARIS, Nov 15 (Reuters) - French judges have issued arrest warrants for Syria's President Bashar al-Assad, his brother Maher al-Assad, and two other senior officials over the use of banned chemical weapons against civilians in Syria, a judicial source said on Wednesday.

The arrest warrants -- which refer to charges of complicity in crimes against humanity and complicity in war crimes -- follow a criminal investigation into chemical attacks in the town of Douma and the district of Eastern Ghouta in August 2013, attacks which killed more than 1,000 people.

It is the first international arrest warrant that has been issued for the Syrian head of state, whose forces responded to protests that began in 2011 with a brutal crackdown that U.N. experts have said amounts to war crimes.

These are also the first international arrest warrants that have been issued over the chemical weapons attack in Ghouta, said Mazen Darwish, lawyer and founder of the Syrian Center for Media and Freedom of Expression (SCM), which filed the case in France.

Syria denies using chemical weapons but a previous joint inquiry of the United Nations and the Organisation for the Prohibition of Chemical Weapons found that the Syrian government used the nerve agent sarin in an April 2017 attack and has repeatedly used chlorine as a weapon.

The Syrian presidency and information ministry did not immediately reply for comment.

"The president is responsible for many crimes in Syria - but with this type of weapon in particular - sarin gas - it's impossible to jump over the gap (of his involvement)," Darwish told Reuters, noting that approval from the president as commander of the armed forces would be mandatory.

Arrest warrants for sitting heads of state are rare because they generally enjoy immunity from prosecution. However, international law has exceptions to that immunity when a head of state is accused of war crimes and crimes against humanity or genocide.

The International Criminal Court currently has two arrest warrants against heads of state: one against sitting Russian President Vladimir Putin and another against former Sudanese president Omar al-Bashir.

Assad was shunned for more than a decade by most countries in the region and the rest of the world, with a few rare trips to Russia and Iran since the war broke out in 2011.

His visit to the United Arab Emirates last year signaled a thaw in relations and was followed by a diplomatic flurry following this year's deadly earthquake in Syria.

He has since been welcomed back into the Arab League and traveled as far as China.

Warrants were issued to Ghassam Abbas, director of the Scientific Studies and Research Centre (SSRC), the agency that established Syria's chemical weapons programme, and Bassam al-Hassan, chief of security and liaison officer.

Assad's brother Maher was deemed complicit in his role as head of the fourth armoured division.

Judges from the crimes against humanity unit at the Paris Tribunal have issued a total of 11 arrest warrants for crimes committed by Syrian officials.

In October, French judges issued warrants for two former defence ministers over a 2017 bomb that killed a French-Syrian man at his home in Daraa.

Photo from AFP