COLOMBO, Sept 18: Sri Lankan troops, locked in heavy fighting with Tamil rebels in Wanni region, have started using gas masks after rebels used “CS” gas against government troops on Monday.

Cornered within the confines of two districts in the Wanni region of northern Sri Lanka, the Liberation Tigers of Tamil Eelam had used a kind of gas on Monday which created breathing problems for government troops in the Akkarayankulam-Vannivilankulam sector.

As many as 16 soldiers had to be flown to a base in Anuradhapura to receive emergency treatment.

Sri Lankan Army Commander Lt-Gen Sarath Fonseka told Daily News newspaper on Thursday that the LTTE had fired two canisters filled with “CS” gas, which is the popular name for 2-chlorobenzalmalononitrile.

The general said that the army was already aware of the possibility of a gas attack and that the troops in the Wanni region had been supplied with gas masks.

Discovered by Carson and Staughton in 1928, CS has been a favourite weapon to neutralise rioters and hijackers. There are 15 varieties of CS, not all of which are harmful. A milder form is used as aerosol. Some varieties can cause allergic dermatitis, vomiting, coughing, breathing difficulties and disorientation.

It was branded as a dangerous chemical weapon and banned in 1997. However, it is still used, because it is preferable to the deadlier nerve gas

It was the breakaway LTTE commander, Col Karuna Amman, who had first alerted the Sri Lankan forces to the possibility of the LTTE using chemical weapons against government troops.

“Prabhakaran (the LTTE leader) had told his commanders once that when cornered, the LTTE would use chemical weapons,” Karuna said in tele-phonic interview on Thursday.

AP ADDS: Sri Lankan naval forces fought a ferocious sea battle with Tamil Tiger separatists off Sri Lanka’s north-western coast on Thursday, sinking 10 boats and killing at least 25 rebel sailors, the military said.

The naval confrontation came as intense ground fighting between military forces and Tamil rebels in the north killed 15 rebels and three soldiers, according to the military. The rebels, meanwhile, said they killed 25 soldiers in fighting on Thursday.