Turkey's main opposition party and a left-wing party have formed an alliance to contest July parliamentary elections.
The Republican People's Party and the smaller Democratic Left Party say they will cooperate to challenge the ruling Islamist-rooted A.K. party of Prime Minister Recep Tayyip Erdogan.
The alliance between the two secularist parties would allow the Democratic Left Party to circumvent a rule requiring parties to win at least 10 percent of the vote before entering parliament.
In another development, a top Turkish prosecutor has ordered the main Kurdish political party, Democratic Society Party, to expel four members who were convicted of links to separatist Kurdish rebels. The four include prominent Kurdish politician and former member of parliament Leyla Zana.
The Kurdish party has said it will field candidates as independents to bypass the 10 percent rule.
Mr. Erdogan called the early elections after parliament failed to elect his party's nominee for president, Foreign Minister Abdullah Gul.
More than one million people took to the streets of Turkey's third-largest city, Izmir, on Sunday to protest Mr. Erdogan's government.
Mr. Erdogan said Wednesday that he supports the country's secular laws. He says his government has done nothing to alter Turkey's secular system during his four-and-a-half years in power.
Some information for this report was provided by AFP, AP and Reuters.
