HAVANA, Cuba (AFP)—Ten Panamanians have been arrested in Cuba for making “subversive” anti-government signs, the interior ministry in Havana said Monday.

The ministry said the ten “had been instructed to enter Cuba for the purpose of making signs with subversive content” on Saturday morning in Havana and had admitted responsibility.

The ministry added that the suspects had been offered between $1,000 and $1,500 each to take part in the alleged operation, the details of which the government did not disclose.

The communist island is on high alert for attack following repeated threats by US President Donald Trump.

Last week, the Cuban coast guard shot dead four people aboard a US-flagged speedboat that came within one nautical mile of Cuba’s shores “for terrorist purposes,” according to Havana.

Six other passengers were injured in the shootout in what Cuba portrayed as an attempted incursion by US-based Cubans aiming to destabilize the government.

At least two of those aboard the speedboat were US citizens, one of whom was killed and the other injured.

The commander of the Cuban coast guard vessel was also injured.