(Adds air raids)

COLOMBO, Jan 31 (Reuters) - A suspected Tamil Tiger suicide bomber blew himself up in a crowded marketplace in northern Sri Lanka on Thursday killing three people, and the air force bombed rebel positions also in far north, the military said.

Thirteen other people, also civilians, were wounded in the blast in Thirunaweli in the northern Jaffna peninsula, where fighting between the military and the Liberation Tigers of Tamil Eelam has escalated in recent weeks.

"The bomber arrived at the site riding a bicycle and exploded himself," military spokesman Brigadier Udaya Nanayakkara said.

There was no immediate comment from the Tigers who have in the past denied attacking civilians.

The military also said air force fighter jets pounded a Tamil Tiger rebel suicide indoctrination centre in the rebel-held northern district of Mullativu.

"The pilots confirmed the base was substantially damaged," said air force spokesman Wing Commander Andrew Wijesuriya.

Separately, five rebels were killed in ground battles on Wednesday in the northern districts of Vavuniya and Polonnaruwa, the military said.

The clashes were the latest in a series of daily sea, land and air battles between the state and Tamil Tiger rebels, which have escalated since a six-year truce was scrapped on Jan. 16. An estimated 70,000 people have died in the two-decade conflict. (Reporting By Ranga Sirilal; Editing by Jon Boyle)

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