Ranil Wickremesinghe vowed not to allow a repeat of 2014 anti-Muslim riots in which four people died and hundreds of homes were destroyed.
“The police as well as all other relevant authorities have been ordered to ensure law and order is maintained,” he said in a special address to the nation.
“We are ready to introduce new laws.”
Wickremesinghe did not give details, but official sources said the government would introduce new provisions to prosecute hate speech.
The pledge followed criticism that police were failing to tackle arson attacks on Muslim homes, shops and a cemetery.
On Sunday, police announced they had arrested a 32-year-old member of the radical Buddhist Force, or BBS, in connection with those incidents and would also question more members of the group.
The BBS was accused of instigating the 2014 religious riots, but it escaped prosecution under the then-strongman president Mahinda Rajapakse.
With stoning and desecration of Muslim-owned places now an almost daily occurence, the government faces international criticism over its failure to tackle the violence and rein in the BBS.
In a video message released Sunday, the group denied any involvement, but accused the government of allowing Islamic extremism to flourish in the Buddhist-majority
nation.
Its leader, Buddhist monk Galagodaatte Gnanasara, has been living underground since May 26 as police investigated more than a dozen complaints of incitement against him.
Earlier this month, Western diplomats urged Sri Lanka to take action to stop the renewed outbreak of religious violence.
The head of the European Union delegation in Colombo, Tung-Lai Margue, said it was crucial there was “no impunity for hate crimes”.
