A fiber-optic cable connecting Cuba to the Internet via Venezuela was completed in February 2011, but testing of the line only began this month, the BBC reported.
Government and research institutions are expected to be the first to make use of the $70 million connection; most Cubans currently have to avail themselves of slow and costly satellite services to go online.
That may be the status quo for some time, as Etecsa said high-speed browsing is unlikely to become widely accessible for some time.
Cuba's infrastructure needs building up, it said, so that Internet access could be offered "gradually" and for "social purposes."
The high-speed Alba-1 cable is a joint venture between the state-owned telecommunications entities of Venezuela and Cuba, with Cuba saying the U.S. trade embargo prevented a link-up to existing American underwater cables.