(Adds Erdogan met military chief, chief prosecutor comments)

By Thomas Grove

ISTANBUL, Jan 22 (Reuters) - Turkish police arrested around 30 people, including army officers and a police chief, in a nationwide sweep on Thursday for suspects in an alleged coup plot that has rattled markets and fuelled tensions with the army.

Eight active army officers and nine police, including special forces officers, were detained, broadcasters said. A search was under way for a military lieutenant in western Turkey, state-run Anatolian news agency said.

A regional police chief and an officer were also taken to Istanbul for questioning, and more detentions were taking place from Bursa in the west to Igdir in the east. The leader of a metal union and a journalist were also arrested and police were searching the offices of the metal union.

Eighty-six people, including retired senior officers, are on trial over their suspected links to a nationalist group known as "Ergenekon". It is accused of plotting to overthrow the Islamist-rooted AK Party government in Turkey, which is a candidate to join the European Union.

A wave of detentions earlier this month, including of active officers, further strained relations between the government and the secular establishment made up of the military and judiciary.

Thursday's detentions included one captain, three lieutenants and four petty officers, broadcaster CNN Turk reported.

An acting chief Istanbul prosecutor said searches completed on Thursday could lead to new arrests and that additional court documents would be prepared within a month in order to try others who have been arrested in the investigation.

Turkey's powerful military, which has unseated governments four times in the past 50 years, has criticised the investigation and denied any links to an alleged plot to conduct bombings and assassinations to clear the way for a coup.

Prime Minister Tayyip Erdogan met Turkey's top military commander General Ilker Basbug for two hours on Thursday in a bid to decrease tensions fuelled by the Ergenekon investigation.

Critics say the governing AK Party is carrying out the arrests as revenge for a 2008 court case that sought to ban the party for anti-secular activities. The AK Party, which embraces centre-right elements and nationalists as well as religious conservatives, denies this. (Editing by Mark Trevelyan)

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