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Erdoğan's AK Party, which has turned Turkey into one of the world's fastest-growing economies, comfortably won a 12 June vote in an outcome investors welcomed as an opportunity to build consensus around government plans to write a new constitution.
But the boycotts by the main opposition Republican People's Party (CHP) and the pro-Kurdish Peace and Democracy Party (BDP) have cast a shadow over the vote's outcome and raised the possibility of massive by-elections.
The CHP won 135 seats in the 550-strong parliament, while the BDP won 36 seats. Taking CHP and BDP together, more than 30% of candidates elected will be boycotting the swearing-in.
"We will not take the oath unless the way is open for all our deputies to take the oath," CHP leader Kemal Kılıçdaroğlu said, after a court rejected an appeal for the release of two of the party's candidates who were under detention without having been convicted.
The BDP announced its decision last week after the Election Commission ruled a candidate must forfeit his seat because of a conviction for spreading "terrorist propaganda" and awarded the seat to a runner-up from AK.
AK, a socially conservative party with Islamist roots, took 326 seats. But the disqualification of opponents is potentially enough to take AK past the 330-seat mark, which would give Erdoğan a larger majority to call a referendum for a planned new constitution without the support of other parties.
The BDP bloc stands to lose another five seats after courts ruled against releasing five other candidates, detained on charges of having ties to Kurdish rebels.
Courts also have blocked a retired general fielded by the far-right Nationalist Movement Party (MHP) from attending because he is detained on charges related to an alleged conspiracy.
The MHP, which won 53 seats, has criticised the ruling but plans to attend parliament.
President Abdullah Gül had appealed to all parties to resolve their differences in parliament, while Turkish investors are monitoring the developments.
"Brinkmanship acts grip Turkish politics," the Daily News said in a headline summing up the atmosphere in Ankara.
The swearing-in ceremony is due to start at 3 p.m. local time (1200 GMT).
AK officials say the Election Commission and courts act independently, but opposition parties are crying foul.
There are no constitutional or parliamentary rules governing what should happen if winning candidates refuse to be sworn in.
There is a rule that if more than 5% of MPs resign their seats will be thrown open for by-elections, but as candidates cannot resign unless they have been sworn-in, it leaves the issue in a grey area.
After the oath-taking, MPs submit applications for the speaker's post. Once a speaker is elected, the next step is for the new government to submit its programme to a confidence vote, after which parliament goes into recess until 1 October.
Parliament sources said the legislature could remain open after a new speaker is chosen to deal with the problems. They said elected MPs could take their oaths at another time.
Any decision to call by-elections would carry the risk of provoking more unrest in the southeast at a time when many people are hoping Erdoğan will revive efforts to heal wounds and grant more rights to Kurds, to end an insurgency that has killed more than 40,000 people.
The PKK ended a six-month ceasefire in February, moving to what it calls an "active defence" stance, whereby its fighters defend themselves if under attack.
With tensions rising, security forces killed three Kurdish militants on Tuesday in the eastern province of Tunceli, where two police were killed last week. On Monday, rebels killed one soldier in an ambush near Turkey's border with Iran.
EurActiv with Reuters