"SriLankan Airlines has observed a drop in traffic between Chennai and Colombo due to recent developments in Tamil Nadu, hence it was decided to reduce its frequency of flights¦" the airline said in a statement.
"Revised schedule involves two daily flights, departing Colombo in the morning and evening, to facilitate the passengers who board their flights to Middle East and far eastern destinations from Chennai.
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Sri Lanka's foreign ministry said it cautioned travellers to Tamil Nadu, while India said those involved in attacks had been arrested.
Indian Tamil activists have attacked unarmed Sri Lankan tourists several times leading to travel advisories from Colombo.
Authorities said 250,000 Sri Lankans travelled to India last year.
"Flights to other Indian destinations will be operated uninterrupted," SriLankan said.
"SriLankan Airlines is closely observing the situation and will take further action if necessary."
South Indian extremist groups have been attacking un