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Catalan separatists are raising questions about the independence of the Spanish judiciary, claiming their jailed leaders are "political prisoners."

Spain's government rejects talk of judicial bias or pressure, stressing that Spain respects the rule of law and does not conduct politically motivated investigations.

It's not the first time the issue of judicial independence has fueled debate in Spain. A look at the controversy and how the Spanish legal system works:

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THE CATALAN CONTROVERSY

The ousted Catalan president Carles Puigdemont, who is on the run from Spain, has said he and four of his Cabinet members dismissed by Spain can't expect a "fair and independent" hearing in Spanish courts.

"There is a clear lack of independence and neutrality, with the links between the judiciary and the government visible for all to see," he wrote on Monday in the Guardian.

Nine other deposed Cabinet members in that same rebellion case were sent to jail in Madrid, eight of them without bail, on preliminary rebellion charges while the judge's investigation continues. Two prominent separatist activists are also in detention.

Catalan separatists insist Prime Minister Mariano Rajoy is using the legal system to persecute them. But the government says it's the courts that have put the officials in jail because they broke he country's laws.

"There are no political prisoners in Spain," Justice Minister Rafael Catala said on Tuesday at the country's Senate. "Neither the government, nor the parliament or anybody else than judges have the power in this country to decide who goes to prison."

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THE COURT SYSTEM

Spain's legal system is governed by the 1978 Constitution, which enshrines the principles of impartiality and independence of the judiciary.

The National Court has jurisdiction over the whole country, and takes on cases that affect more than one region. Because it rules on serious graft crimes, terrorism and international cases, its decisions are often closely scrutinized.

Decisions can be appealed to the Supreme Court, the highest judicial body, which also tries lawmakers and other officials. Its rulings can only be appealed to the Constitutional Court.

The Constitutional Court settles when lower legislation exceeds its limits, and rules on matters from abortion to same-sex marriage and bullfighting.

Each province also has its own district and provincial courts and each of Spain's 17 autonomous regions have high tribunals.

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HOW ARE JUDGES APPOINTED?

Critics have long argued that Spain's politics and the courts are too entangled.

The Constitutional Court's 12 members are appointed by the General Council of the Judiciary, the government and parliament's two chambers, usually controlled by either of the two parties that have taken turns in power over four decades.

The General Council is also in charge of picking, training, promoting and sanctioning Spanish magistrates, as well as appointing the presiding judge at the country's powerful National Court and at all the high tribunals in each of the 17 regions.

The council has 21 members — half are elected by parliament and half by the Senate, where the two main political parties have the upper hand.

Its president is the head of the Supreme Court.

A report published last year by the Council of Europe noted that officials on the council are appointed by the country's main political parties. The linkage is "so obviously ... political" it amounts to "a potential threat to judicial independence."

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WHAT ABOUT THE PROSECUTORS?

Spain's chief prosecutor is formally appointed by the king, after being selected by the government and confirmed by a simple majority at a parliamentary committee.

By law, the position requires impartiality from its holder, currently Jose Manuel Maza, and is independent of other state powers.

Politicians say more lawmakers need to have a say over the appointment of such a key position. They also propose the uncoupling of the position's term from that of the government's. But no parties have actually initiated the body's reform when in power.

That has led to the recurring criticism that the top prosecutor doesn't defend the public interest and is at the service of the government instead.

Although many powerful figures, including Spain's Princess Cristina and former IMF chief Rodrigo Rato, have recently been brought to Spain's courts, critics say most of those cases were brought by individuals or public organizations, not by the public prosecutor.

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TRAILING BOTTOM IN EUROPE

Results from a 2015 report from the European Network of Councils for the Judiciary, a group representing national judiciaries at the EU, show Spain ranks near bottom in judicial independence.

A survey of hundreds of European judges showed that 15 percent of Spanish judges agreed they had been under inappropriate political pressure over their work in recent years. Only Albania and Latvia did worse.

Spain also had more judges than any other European country say they had been allocated cases to influence the outcome of particular lawsuits.

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"INDIVIDUALLY INDEPENDENT"

Miguel Pallares, spokesman of the main association of prosecutors in the country, says that the politicization of top appointments at both the General Prosecutor's Office and the General Council of the Judiciary casts a shadow over the fair work usually carried out by attorneys, judges and courts.

Ignacio Gonzalez, spokesman for Judges for Democracy, an association of magistrates, disagreed.

"The main problem is the perception among citizens of the lack of independence," Gonzalez says. "But judges are individually independent, and there are enough mechanisms to disqualify them if their impartiality is in question."

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Hatton reported from Lisbon, Portugal.