Turkish police say they are hunting two suspects over an explosion in the resort town of Antalya that left three dead and hurt at least 20 on Monday.
Many people were hurt by flying glass and shrapnel in Antalya
The blast came hours after at least 27 people were hurt when bombs exploded in Istanbul and the resort of Marmaris.
A Kurdish militant group linked to the banned PKK party has said it carried out all three attacks.
Security has been tightened on Turkey's Mediterranean and Aegean coasts as police hunt the attacks' perpetrators.
On Monday night, police revealed they had arrested a man in Izmir accused of being involved in a failed plot to bomb the western coastal town.
The Turkish state news agency said the man was from the Kurdistan Workers Party (PKK) separatist group.
It said other people were also detained for helping the suspect and that plastic explosives were seized in the operation.
The Turkish economy is heavily reliant on tourism, which Kurdish separatists have repeatedly threatened to target.
Struck by glass
The authorities have yet to say whether the Antalya blast was caused by a bomb but correspondents say the news that they are hunting for two suspects suggests this was the case.
ATTACKS IN TURKEY
27 August: 21 injured in three blasts in Marmaris
27 August: Six wounded in blast in Istanbul
25 June: 4 killed, 25 injured in southern resort of Antalya
16 April: 31 injured in Bakirkoy district of Istanbul
31 March: 1 killed, 13 injured in Istanbul's Kocamustafapasa district
9 February: 1 killed, 16 injured at internet cafe in Istanbul's Bayrampasa district
18 November: One killed and 11 injured in the Beylikduzu district of Istanbul
A police spokesman said 20 people were hurt in the blast, which took place on Monday afternoon in a busy shopping area in the city.
The Dogan news agency said the total number of injured - including those who had suffered light wounds - was 71.
The force of the blast ripped off the facade of a municipal building and badly damaged nearby shops and restaurants and sparked a fire.
Many passers-by were struck by glass and shrapnel.
A Kurdish militant group with links to the banned PKK has claimed responsibility for Sunday's blasts in Marmaris and Istanbul.
"We had warned before, Turkey is not a safe country. Tourists should not come to Turkey," the Kurdistan Freedom Falcons (Tak) said on its website.
On Tuesday, the group also claimed responsibility for the Antalya attack.
Wave of bombings
Most of those injured in Marmaris - including 10 Britons - were on a minibus ferrying local people and holidaymakers along the main street.
Istanbul was also hit by a bomb attack on Sunday night, when a roadside device exploded injuring six Turkish nationals.
Both Marmaris and Antalya are popular with European and Russian holidaymakers.
The attacks are the latest in a wave of similar bombings in Turkey in recent years, blamed on either Kurdish separatists, Islamic militants or left-wing extremists.
Four people - including three foreigners - were killed in an explosion in Antalya in June. Initial investigations suggest a gas canister exploded, but doubt was cast over whether it had been an accident.