JAKARTA (Reuters) - Indonesia booked a $3.45 billion merchandise trade surplus in January, bigger than expected, amid surprisingly weak imports, official data showed on Monday.

A Reuters poll of analysts had expected a surplus of $1.91 billion for January.

Imports last month were worth $18 billion, down 2.67% from the same month a year earlier, in contrast with analysts' forecast of a 9.95% growth.

Exports rose 4.68% on an annual basis in January to $21.45 billion, compared with 6.99% growth expected in the poll.