The US ambassador to Sri Lanka said on Tuesday that some of the 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 start of Ramazan, which is supposed to begin next Monday.

“Tremendous progress has been made towards 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 militants 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 Ramazan.

Teplitz said 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 FBI is assisting Sri Lankan authorities in the investigations but Teplitz declined to give more details.

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.