ISTANBUL (Reuters) - The lawyer for the American Christian pastor on trial for terrorism charges in Turkey said on Wednesday he planned to appeal to the constitutional court to seek Andrew Brunson’s release after being rejected by a lower court last week.

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Brunson is at the center of a row between Turkey and the United States, which has exacerbated a crisis in Turkey’s lira and reverberated across global markets.

The evangelical pastor, who has lived in Turkey for two decades, has been detained for 21 months on terrorism charges, which he denies. He is under house arrest.

“Once the upper court’s rejection has been confirmed in writing we will apply to the constitutional court,” lawyer Ismail Cem Halavurt said in comments reported by Turkey’s Hurriyet newspaper that he confirmed to Reuters.

Once domestic legal avenues are exhausted, if necessary the defense would then apply to the European Court of Human Rights (ECHR), he said.

“We are hopeful regarding the constitutional court, but if it is rejected there, we will go to the ECHR without hesitation,” he said.

The court in Turkey’s Izmir province which last week rejected the appeal said evidence was still being collected and the pastor posed a flight risk, according to a copy of the court ruling seen by Reuters.

Abdulkadir Selvi, a Hurriyet newspaper columnist close to the government, likened the constitutional court appeal plan to the case of journalist Mehmet Altan, who took a similar course of action and was released in June after being jailed on charges of aiding coup plotters.

Brunson is accused of terrorism charges and aiding the network of a U.S.-based Islamic preacher blamed by Ankara for masterminding a coup attempt in July 2016 against President Tayyip Erdogan.

In an interview with Reuters on Monday, U.S. President Donald Trump said he would give Turkey no concessions in return for the release of Brunson. Ankara has not responded to Trump’s comments.

Trump, who counts evangelical Christians among his core supporters, has become a vocal champion of the pastor’s case.