COLOMBO • Sri Lankan security officials yesterday warned that Islamist militants behind the Easter Sunday suicide bombings are planning more attacks and could be dressed in uniform, as the authorities banned women from wearing face veils under an emergency law put in place following the attacks.

"There could be another wave of attacks," the head of the police Ministerial Security Division said in a letter to lawmakers and other officials seen by Reuters.

Officials said the militants behind last Sunday's suicide bombings on hotels and churches, which killed more than 250 people, could be planning to use military disguises.

"The relevant information further notes that persons dressed in military uniforms and using a van could be involved in the attacks," the letter said.

Five locations were targeted for the attacks, which were to be carried out on Sunday or yesterday, security sources said.

There were no attacks on Sunday and security across Sri Lanka has been ramped up, with scores of suspected militants arrested.

The authorities believe Zaharan Hashim, the founder of the little-known National Thowheeth Jama'ath, was the mastermind of the Easter Sunday attacks and one of the nine suicide bombers.

Prime Minister Ranil Wickremesinghe said a tight-knit group was involved, mostly friends and families who spoke face to face, possibly to evade electronic surveillance.

President Maithripala Sirisena on Sunday announced the government has banned women from wearing face veils.

The authorities said the move would help security forces identify people, as a hunt for any remaining attackers and their support network continues across the Indian Ocean island.

"The ban is to ensure national security... No one should obscure their faces to make identification difficult," the statement said.

It came days after local Islamic clerics urged Muslim women not to cover their faces amid fears of backlash, after the bombings by militants affiliated with the Islamic State in Iraq and Syria (ISIS).

Separately, Mr Wickremesinghe, who is feuding with Mr Sirisena, issued a statement saying he had asked the justice minister to draft regulations to ban the burqa.

But the moves have led to concerns within the Muslim community that a prolonged ban could fuel tensions in the religiously diverse nation, which emerged from a civil war with ethnic minority Tamil separatists a decade ago.

The All Ceylon Jamiyyathul Ulama (ACJU), the top body of Islamic scholars in Sri Lanka, said it supported a short-term ban on security grounds, but opposed any attempt to legislate against burqas.

"We have given guidance to the Muslim women to not cover their faces in this emergency situation," ACJU assistant manager Farhan Faris said, after the scholars asked the government to drop plans for a law against the burqa and niqab.

"If you make it a law, people will become emotional and this will bring another bad impact... It is their religious right," he told Reuters.

About 9.7 per cent of Sri Lanka's roughly 22 million people are Muslim. Only a small minority of women, usually in Muslim areas, fully hide their faces.

The Archbishop of Colombo, Cardinal Malcolm Ranjith, yesterday said there remained insufficient security around churches in the island, and urged the authorities to ensure their safety.

Many Sri Lankans believe the rift between Mr Sirisena and Mr Wickremesinghe has undermined national security.

Mr Sirisena fired Mr Wickremesinghe last year after months of tension, only to be forced to reinstate him under pressure from the Supreme Court.

Since then, their relationship has deteriorated further to the point where their factions actively try to undermine each other, such as by not sharing security information, defence sources say.

Mr Sirisena said yesterday he had appointed Mr Chandana Wickramaratne, the second in command at the police, as acting police chief.

Over the weekend, sources at the President's office told Reuters that Mr Pujith Jayasundara, the police chief appointed by Mr Wickremesinghe, was refusing the President's request to step down for not sharing details of the attacks.

"Since there is an investigation into his possible failure in preventing the attacks, Jayasundara has been sent on compulsory leave," a source close to the President told Reuters. The President has also appointed General Shantha Kottegoda as the new defence secretary, replacing Mr Hemasiri Fernando, who resigned after the bombings.

Mr Kottegoda, 69, was an army commander between 2004 and 2005. He was instrumental in weakening the Tamil Tiger rebels by breaking away an allied group.

REUTERS, AGENCE FRANCE-PRESSE