By A. Ananthalakshmi and Alexandra Ulmer

COLOMBO (Reuters) – The U.S. ambassador to Sri Lanka said on Tuesday that some of the Islamist militants behind Easter Sunday bombings that killed more than 250 people were likely still at large and could be planning more attacks.

Sri Lankan security forces also said they were maintaining a high level of alert amid intelligence reports that the militants were likely to strike before the beginning of the Islamic holy month of Ramadan, which is due to begin next Monday.

“Tremendous progress has been made toward apprehending those plotters but I don’t think the story is over yet,” Ambassador Alaina Teplitz said in an interview.

“We do believe that there is active planning under way,” she said, referring to the possibility of more attacks.

Scores of suspected Islamists have been arrested in the multi-ethnic island nation since April 21 suicide bomb attacks on hotels and churches. Among the dead were 42 foreign nationals.

“Security will stay tight for several days because military and police are still tracking down suspects,” a senior police intelligence official said. 

Another government source told Reuters security authorities had ordered police and other security forces across the Buddhist-majority country to remain on high alert because the militants were expected to try to strike before Ramadan.

Teplitz told Reuters the risk of more attacks remained real.

“We certainly have reason to believe that the active attack group has not been fully rendered inactive,” she said.

The U.S. Federal Bureau of Investigation is assisting Sri Lankan authorities in the investigations but Teplitz declined to give more details.

The State Department has issued a travel advisory suggesting people reconsider plans to travel to Sri Lanka.

SOCIAL MEDIA BAN LIFTED

The government has lifted a ban on social media platforms such as Facebook, WhatsApp and Viber, a source at the president’s office said. The ban was imposed immediately after the attacks to prevent the spread of rumors.

The government has also banned women from wearing face veils under an emergency law invoked in response to the blasts.

Authorities suspect members of two previously little-known groups – National Thawheedh Jamaath (NTJ) and Jammiyathul Millathu Ibrahim – of carrying out the attacks, although the Islamic State militant group has claimed responsibility.

Authorities believe Zahran Hashim, the founder of NTJ, was the mastermind and one of the nine suicide bombers.

Islamic State released a video after the attack through its AMAQ news agency, showing eight men, with all but Zahran with their faces covered, standing under a black Islamic State flag, declaring loyalty to its leader, Abu Bakr al-Baghdadi.

The Islamic group’s media network published a video on Monday purporting to come from al-Baghdadi, in which he said the Sri Lanka bombings were Islamic State’s response to losses in its last stronghold of Baghouz in Syria.

In India, police said they had arrested a 29-year-old man in the southern state of Kerala, close to Sri Lanka, for planning similar attacks there. The man had been influenced by speeches made by Zahran, India’s National Investigation Agency said in a statement.

Sri Lanka’s 22 million population is mostly Buddhist but includes minority Christians, Muslims and Hindus.

(Additional reporting by Ranga Srilal and Shri Navaratnam; Writing by Raju Gopalakrishnan; Editing by Paul Tait and Nick Macfie)