Tomorrow's protest in Izmir, Turkey's third largest city, is aimed at putting pressure on the Islamist-rooted government and uniting the opposition amid rising political tensions ahead of an early general election on July 22.
''The bomb exploded on a bicycle ... The injured are being treated at two local hospitals,'' a police spokesman said.
The semi-official Anatolian news agency reported that one person who had been in critical condition died from injuries, but police could not immediately confirm the death.
The police spokesman said nobody was riding the bike at the time of the blast, which occurred early in the morning when there were relatively few people in the area. Most of the injured were tradespeople working at the market, in the Bornova district of the city.
Local police called for blood donations.
Nobody has claimed responsibility for the bomb, which is thought to have been fastened to the bicycle.
Izmir's mayor, Aziz Kocaoglu, played down any possible connection between the blast and Sunday's rally.
''The bombing should not be linked to the rally tomorrow. I don't think anyone will refuse to go to the rally because of this,'' Kocaoglu told the Anatolian state news agency.
Some local people said the blast had hardened their determination to attend the rally, which organisers say could draw up to two million people opposed to the Islamist-rooted government of Prime Minister Tayyip Erdogan.
''I think this explosion is a terrorist provocation. Tomorrow I am going to take up the flag. We will all come together at the rally because we are all Turkish,'' said vendor Guven Gutlu, 41.
Many accuse the ruling AK Party of having a hidden agenda to erode Turkish secularism, a charge which it strongly denies.
''Turkey is a secular republic ... and it cannot be divided,'' said Erdogan today, speaking at a rally for his AK Party in central Anatolia. Tens of thousands attended the first campaign rally for the party ahead of early elections in July.
KURDISH LINK? ''It could be the PKK (Kurdish militants) but we don't know,'' said Gutlu, adding that one of his friends had been hurt in the explosion. Gutlu himself had been about 100 metres (yards) away.
Kurdish militants have in the past carried out small attacks in the Izmir area, which is home to a large Kurdish population and also a major port of entry for European tourists visiting Turkey's Aegean coast.
The Kurdish militants have pledged in the past to disrupt Turkey's highly lucrative tourist industry.
Political tensions are running especially high after Erdogan's ruling AK Party clashed with the country's powerful secular elite, including army generals, over a presidential election in parliament.
Public rallies, a court ruling and a strong statement from the army General Staff forced the government to withdraw its presidential candidate, Foreign Minister Abdullah Gul, an ex-Islamist, and call an early parliamentary election for July.
Leaders of Turkish centre-left opposition parties will attend tomorrow's rally. It comes after a recent rally in Istanbul attracted one million people, many middle class secular urban Turks concerned about the direction of the country.
Secularists accuse the AK Party of planning to undermine Turkey's strict separation of state and religion. The AK Party, which has presided over strong economic growth and the launch of Turkey's European Union entry talks, strongly denies the claim.
''The bombing makes us afraid,'' said Yigit Katuk, a high school student, who lives near the blast area. ''Our republic is under threat, that's why I'm going with my whole family.'' REUTERS SKB PM2030