COX'S BAZAR - Social network Facebook and its messaging app have been down in Bangladesh since Friday, the U.S. tech giant said on Saturday, as protesters oppose Indian Prime Minister Narendra Modi's two day visit to the country.

Four people were killed on Friday after police opened fire after protesters allegedly attacked a police station in the Bangladeshi city of Chittagong during a demonstration against Modi's visit.  

"We're aware that our services have been restricted in Bangladesh," Facebook said in a statement. "We're working to understand more and hope to have full access restored as soon as possible."

The government of Prime Minister Sheikh Hasina did not comment if it had blocked Facebook and its messenger, but it has previously used internet shutdowns as a tool to curb the spread of protests.

Facebook also said it had serious concerns about the manner in which it was being restricted in Bangladesh at a time when effective communication was necessary to tackle the coronavirus pandemic.

Local hardline group Hefazat-e-Islam, meaning protection of Islam, has called for a nationwide strike on Sunday to protest the Chittagong killings. Hefazat and its supporters accuse Modi of alienating minority Muslims in India.

Modi landed in Dhaka on Friday for a two-day visit, his first international trip since the outbreak of the coronavirus pandemic last year, to celebrate the 50th anniversary of the nation's independence.

He is due to hold formal talks with Hasina on Saturday.

(Reporting by Ruma Paul in Dhaka, Devjyot Ghoshal in New Delhi; Writing by Sankalp Phartiyal; Editing by Michael Perry) ((sankalp.phartiyal@thomsonreuters.com; +91-11-49548064;))