UPDATE 2-Thousands of Brotherhood supporters in Turkey mourn Egypt's Mursi

(Adds Erdogan quotes)

By Ece Toksabay and Ali Kucukgocmen

ANKARA/ISTANBUL, June 18 (Reuters) - Thousands of supporters of the Muslim Brotherhood in Turkey took to the streets of capital Ankara and Istanbul on Tuesday to mourn former Egyptian president Mohamed Mursi, with some chanting slogans blaming Cairo authorities for his death.

Mursi, a leading member of the Islamist group which is now banned in Egypt, died on Monday after collapsing in a Cairo court while on trial on espionage charges.

The 67-year-old - the first democratically elected head of state in Egypt's modern history - had been in jail since the army commanded by Egypt's current president Abdel Fattah al-Sisi toppled him in 2013 after barely a year in power following mass protests against his rule.

Turkish President Tayyip Erdogan's Islamist-rooted AK Party supported Mursi’s short-lived Egyptian government, and many Brotherhood members and supporters have fled to Turkey since its activities were banned in Egypt.

Speaking after afternoon prayers at a mosque in Istanbul's conservative Fatih district as part of a commemoration, Erdogan called Mursi a "martyr" and said he doubted that Mursi had died of natural causes.

"It makes one think if this is a normal march (to God) or if there is another situation. Personally, I do not believe that is a normal death," he said. "Long live hell for tyrants."

Earlier in the day, he condemned western countries, saying they had "watched Mursi taken down in a coup and tortured in a prison cell".

About 500 people in Ankara prayed in a central street halting traffic outside the Egyptian Embassy, and in Istanbul hundreds of people attended a symbolic funeral in the conservative Fatih district.

By contrast, in central Cairo on Tuesday morning there were no signs of protests. Egypt has cracked down on Islamist groups since Mursi's ousting.

"MARTYR MURSI"

Members of the Ankara crowd chanted: "Murderer Sisi, martyr Mursi" and held up banners reading "Putschists will be defeated", a reference to Mursi's overthrow.

"We will take back our country from the military coup, and that day, we will go to the tomb of Muhammed Mursi and pray to thank him for staying in prison for six years to free our country of tyrants," said Mumin Ashraf, 25, an Egyptian man studying in Ankara.

Rights groups have called for an investigation into Mursi's death and raised questions about his treatment in prison. Egypt's government has dismissed accusations that he was badly treated.

The Brotherhood says it is a non-violent movement and denies any relationship to violent insurgencies waged by al Qaeda and Islamic State.

Brotherhood spokesman Talaat Fahmi blamed the Egyptian government for Mursi's death.

"Those coup leaders have ... implemented an incremental killing process throughout six years," he told Reuters in an interview in Istanbul.

"They did not allow anyone to witness the funeral. They did not allow anyone to see the body."

(Reporting by Ece Toksabay in Ankara and Ali Kucukgocmen in Istanbul; Additional reporting by Bulent Usta Writing by Humeyra Pamuk; Editing by John Stonestreet and Ed Osmond)