TUNIS, Tunisia (AP) _ Homemade bombs exploded at four coastal tourist hotels and injured 13 people on the eve of national celebrations for President Habib Bourguiba's 84th birthday, officials said Monday.

Except for one Tunisian, all of those hurt were British and Italian visitors. The most seriously injured, Helen Strocki, 28, of Scotland, had her foot amputated, the British Foreign Office said.

There was no immediate claim of responsibility for the bombings. There was no indication they might have been timed to coincide with Monday's celebration or linked to recent unrest reportedly inspired by Islamic fundamentalists.

Ms. Strocki was among four Britons injured when a bomb went off at about 11 p.m. Sunday in the bar of the Sahara Beach Hotel in Monastir, said Jeremy Larner, the British consul in Tunis.

Monastir, 100 miles south of Tunis, is Bourguiba's birthplace and official summer residence.

Larner said seven Italian tourists were wounded in a nearly simultaneous bombing at the Hannibal Palace Hotel in Sousse, about 20 miles north of Monastir.

He said bombs at El Hana Beach Hotel in Sousse and the Kuriat Palace Hotel in Monastir caused no injuries.

A fifth British visitor and a Tunisian also were among the injured, the official TAP news agency reported, without saying where the injuries occurred.

A waiter at El Hana Beach noticed the device there and carried it out to a garden where it exploded harmlessly, Larner said.

The Italian air force said it sent a DC-9 to Tunisia with two doctors and a nurse aboard to bring back Italian wounded.

Britain warned citizens planning trips to Tunisia to exercise caution.

In a statement published by TAP, Tunisia's Interior Ministry said the bombings were ''isolated acts which in no way disturbed the serenity nor the tranquillity in which the entire country is living.''

The statement described the bombs as weak and homemade, but it gave few details.

Recent disturbances officially attributed to Islamic fundamentalists have occasionally spilled into the streets in clashes with police.

Tunisia broke diplomatic relations with Iran in March, saying Iran's embassy was being used to foment trouble among fundamentalists.

According to TAP, celebrations marking Bourguiba's birthday were held in Monastir without incident Monday, despite the bombings. Bourguiba has governed this North African nation for 30 years.