Cuba said the speedboat carrying weapons came from the United States to sow chaos. However, US Secretary of State Marco Rubio said it was not a US operation.Prosecutors in Cuba on Tuesday charged six Cuban nationals with "crimes of terrorism" and accused them of entering Cuba with a US-flagged boat packed with weapons to stir unrest in the country. Their boat was intercepted by Cuba's coast guard as it entered Cuban waters last week, resulting in a shootout. Four of the Cuban nationals aboard the speedboat were killed in the incident and six others were wounded. Last Wednesday, Cuba's Interior ‌Ministry accused the Cuban exiles of opening fire on a border guard vessel, and said they came from the United States with the intent to target military units on the Communist-ruled island. Cuban officials said the boat was carrying firearms of various calibers, including 14 rifles, 11 pistols and nearly 13,000 rounds of ammunition. What do we know about the incident? The firefight began when the coast guard vessel approached the speedboat to demand identification, and they responded by opening fire. The officials also showed pictures of the vessels, which had bullet holes from the shootout they said took place at a range of 20 meters (66 feet). Cuban forces returned fire and took the six survivors into custody, they said. At least two of those taken into custody had prior record of being accused of terrorism, Cuba said. If convicted, they could face prison terms of up to 10 to 15 years for the lesser ⁠offenses and 20 to 30 years — or even the death penalty — for the more serious ⁠charges, Prosecutor Edward Robert Campbell said. The incident comes at a time of heightened tensions between Cuba and the US, with the latter halting all oil shipments ‌to the island country. Political leaders in the US have expressed skepticism over Cuba's version of events, calling for independent investigations. Secretary of State Marco Rubio it was not a US operation and that no US government personnel were involved. Edited by: Zac Crellin