BOSTON (AP) - The lone surviving suspect in the Boston Marathon bombing remains in serious condition at a hospital under heavy guard.

A spokeswoman for the US attorney's office in Boston gave an update on Sunday on the condition of Dzhokhar Tsarnaev.

The 19-year-old Tsarnaev was hospitalised on Friday after being pulled from a boat in a Watertown backyard. His 26-year-old brother, Tamerlan, died in a gunbattle with police.

Massachusetts Governor Deval Patrick said on Saturday that Tsarnaev is apparently unable to communicate at the moment.

There was no immediate word on when Tsarnaev might be charged and what those charges would be. The twin bombings killed three people and wounded more than 180.