Fugitive former Sri Lankan President Gotabaya Rajapaksa is expected to end his self-exile in Thailand and return home soon, authorities told AFP.

Rajapaksa, 73, left the island under military escort in July when crowds of protesters stormed his official residence after months of demonstrations that blamed him for the country's unprecedented economic crisis.

He submitted his resignation in Singapore and then flew to Bangkok, from where he asked his successor to facilitate his return, now scheduled for late Friday evening or early Saturday.

Sri Lanka's constitution guarantees bodyguards, a car and housing for former presidents.

Human rights activists said they would seek Rajapaksa's arrest for a range of crimes, including his alleged role in the 2009 murder of prominent newspaper editor Lasantha Wickrematunge.

Rajapaksa's resignation ended his presidential immunity, which could lead to the reopening of long-running criminal cases against him.

Singapore refused to renew Rajapaksa's short stay visa and he traveled to Thailand in August, but was ordered by Bangkok authorities not to leave his hotel for his own safety.

Rajapaksa's younger brother, Bazil, a former finance minister, met Sri Lankan President Ranil Wickremesinghe in August and asked for protection to allow the ex-president to return.

On Friday, police deployed plainclothes officers and armed guards outside the government residence assigned to Rajapaksa in Colombo. Security at his private home has also been tightened, officials said.

Police at Colombo's main airport said a security operation was underway to prepare for his arrival.