A banned radical Turkish Marxist group retracted its claim for a suicide bombing in the heart of Istanbul's tourist district, raising Saturday the possibility of a jihadist link to the attack that left one policeman and the bomber dead.

Reports earlier this week suggested Tuesday's attack was carried out by a Russian woman from the Muslim Caucasus region of Dagestan, and not the female bomber that the far-left militant group initially said had executed the strike.

An outlawed Turkish Marxist group on Wednesday said one of its members carried out the deadly suicide bombing at the heart of Istanbul's tourist district that killed the female bomber and a policeman.

The Marxist Revolutionary People's Liberation Party–Front (DHKP-C) said in a statement on its website "our sacrificial fighter... carried out the sacrificial action on the tourist police department in Sultanahmet."

A female suicide bomber on Tuesday blew herself up in the most-visited tourist district of Istanbul, killing herself and a Turkish policeman, officials said.

The woman went into the police station in the Sultanahmet district and told the police in English she had lost her wallet before setting off her explosives, governor Vasip Sahin said on Turkish television. 

Heavy snowfall descended on large parts of Turkey on Tuesday, snarling road and air traffic and leading to closures of schools, reports said. 

In the northern province of Karabuk, a school bus went off the road and turned over on to its side in slick conditions caused by snow, leaving a student dead and 18 others injured, the Dogan news agency reported. 

Turkish President Recep Tayyip Erdogan on Saturday praised as "clean and lawful" the legal process against his opponents that has been sharply criticised by the EU and includes an arrest warrant for his arch-foe Fethullah Gulen.

"I have been watching this process closely as president of this country. Everything is lawful and in line with procedure ... a really diligent and clean process is going on at the moment," Erdogan said in a televised speech in Istanbul.

Turkish police on Sunday launched a sweeping operation to arrest dozens of supporters of President Recep Tayyip Erdogan's rival, U.S.-exiled imam Fethullah Gulen, including a raid on the offices of the Zaman daily, which is close to the cleric. 

The operation came just two days after Erdogan signalled a new crackdown against the supporters of Gulen, who Erdogan blamed for orchestrating a corruption probe almost exactly a year ago against members of his inner circle. 

Turkish prosecutors on Wednesday sought life imprisonment for a police officer accused of beating a teenager to death during last year's mass anti-government protests, media reported.

Ali Ismail Korkmaz, 19, died after being pummeled with baseball bats and truncheons in the western city of Eskisehir on June 2.

Turkish President Recep Tayyip Erdogan on Tuesday hit back at ridicule of his claim that Islamic explorers discovered the Americas three centuries before Columbus, accusing his Muslim critics of lacking "self-confidence".

In an aggressive rebuttal of the criticism heaped in some quarters on his comments, Erdogan also suggested that the purported "discovery" of the Americas by Muslims should be taught in schools.

Turkish President Recep Tayyip Erdogan said Saturday that the Americas were discovered by Muslims in the 12th century, nearly three centuries before Christopher Columbus set foot there.

"Contacts between Latin America and Islam date back to the 12th century. Muslims discovered America in 1178, not Christopher Columbus," the conservative president said in a televised speech during an Istanbul summit of Muslim leaders from Latin America.

A group of nationalist Turkish youths on Wednesday attacked three visiting U.S. sailors in Istanbul, trying to force sacks on their heads in an assault angrily condemned by the U.S. embassy.

Several dozen members of the nationalist youth group Turkiye Genclik Birligi (Turkish Youth Union/TGB) attacked the sailors in the Eminonu district on the Istanbul waterfront, a popular tourist hub.