It could be one of the strangest naval encounters in recent history.
Narco submarines have been the bane of counter-narcotics operations on the high seas in recent years.
But coast guard forces more usually deploy aircraft and fast patrol boats to intercept them, rather than tall ships fitted with more than 1,400 square metres of sail – as in the case of the Ecuadorean ship involved, the BAE Guayas.
Narco submarines are thought to have been used by drug cartels since the 1980s, but no interceptions were made by police until 2006 when the US Coast Guard seized one near Costa Rica.
The semi-submersed speed boats are sometimes big enough to carry several tonnes of drugs, taking advantage of a low profile in the water in order to be hard to detect visually or by radar.
On October 20, the Costa Rica Coast Guard intercepted a narco submarine with nearly two tonnes of cocaine on board.
The BAE Guayas, which was built in 1977 as a training ship for cadets, pulled up alongside the vessel.
Its crew held “three Ecuadorians and one Colombian in international waters, near Columbia’s Exclusive Economic Zone”, reported Ecuadorean publication Expreso, on Saturday.
The Ecuadorean Navy confirmed the arrest of the four suspects in a tweet on Saturday.
Authorities said the men had been taken to the mainland for questioning.