Buses carrying Muslim voters in northern Sri Lanka were attacked by gunfire and stones and blocked by burning tires hours voting began in Saturday’s presidential elections, according to a group monitoring election violence.

There were no reported injuries and police were investigating, said Manjula Gajanayake, spokesman for the Colombo-based Centre for Monitoring Election Violence.

Campaigning was dominated by concern over national security in the backdrop of the deadly Islamic State-inspired suicide bomb attacks on Easter Sunday that killed 269 people.

Fears also remained among both minority Tamils and Muslims about a return to power of Gotabaya Rajapaksa, a hard-line former defence official under his brother, ex-President Mahinda Rajapaksa.

Mr Rajapaksa had been widely expected to triumph over the ruling party candidate, Housing Minister Sajith Premadasa, but closer to polling day the race appeared very close.

Mr Premadasa’s supporters organised the bus convoy of Muslims who had fled their homes in the northern district of Mannar in 1982, when the separatist insurgency of Tamil rebels began to grow.

The Elections Commission had encouraged them to register as voters in Mannar but had not arranged enough transportation to bring them from their homes in the northwestern district of Puttalam, Mr Gajanayake said.

It wasn’t immediately clear whether any of the attackers had been arrested.

Nearly 16 million of Sri Lanka’s 22 million people were eligible to vote and choose a new president from a record 35 candidates. President Maithripala Sirisena, who was elected in 2015, is not seeking reelection. Results are expected as early as Sunday.

A decade of peace following nearly 30 years of civil war was shattered earlier this year when homegrown militants pledging loyalty to the Islamic State group detonated suicide bombs at three churches and three hotels on April 21.

Mr Rajapaksa, 71, cast himself as the only candidate capable of protecting Sri Lankans from such attacks.