09:12 GMT - WELCOME TO AFP'S LIVE REPORT following an explosion in Istanbul's Sultanahmet tourist district, with reports saying several are dead and wounded.
Television reports say ambulances and police have been dispatched to Sultanahmet, the Turkish city's main tourist hub, which is home to world-famous monuments including the Blue Mosque and the Hagia Sophia.
Series of attacks
09:19 GMT - Today's blast comes after a series of deadly attacks across Turkey in past months that have left the country's largest city on edge.
The force of the blast was sufficient to be heard in adjacent neighbourhoods, witnesses tell AFP.
09:21 GMT - Turkey has been on alert since 103 people were killed on October 10 when two suicide bombers attacked a crowd of peace activists in the capital Ankara, the bloodiest strike in the country's modern history.
That operation was blamed on Islamic State (IS) jihadists, as were two other bloody assaults in the country's Kurdish-dominated southeast earlier in the year.
09:24 GMT - Turkish authorities have in recent weeks detained several suspected IS members, with officials saying they were planning attacks in Istanbul.
But Turkey is also waging an all-out assault on the outlawed Kurdistan Workers' Party (PKK) which has staged dozens of deadly attacks against members of the security forces in the southeast of the country.
09:25 GMT - A Kurdish splinter group, the Freedom Falcons of Kurdistan (TAK) claimed a mortar attack on Istanbul's second international airport on December 23, which killed a female cleaner and damaged several planes.
The banned ultra-left Revolutionary People's Liberation Party–Front (DHKP-C) has also staged a string of usually small-scale attacks in Istanbul over the past months.
09:31 GMT - Several people have been killed and others wounded in the blast in Istanbul's Sultanahmet district, television reports say.
Authorities are studying the possibility the explosion was caused by a suicide bomber but there is no official confirmation of this or of the number of casualties.
09:33 GMT - TEN KILLED, 15 WOUNDED IN ISTANBUL BLAST, SAY LOCAL AUTHORITIES
09:39 GMT - Ten people have been killed and 15 wounded in the blast in Istabul's Sultanahmet district, the governor's office says.
"Investigations into the cause of the explosion, the type of explosion and perpetrator or perpetrators are under way," it says in a statement quoted by the Dogan news agency.
09:43 GMT - TERROR LINK SUSPECTED IN ISTANBUL BLAST: TURKISH OFFICIAL
09:51 GMT - Turkish authorities suspect a terror attack was the cause of today's deadly blast that has left 10 people dead, a government official says.
"Terrorist links are suspected," the official tells AFP, asking not to be named, after the explosion in the historic Sultanahmet district.
09:58 GMT - The authorities are being circumspect on the precise cause of the blast. Some TV channels say it was a suicide bombing but this has yet to be confirmed, although officials tell AFP they suspect a terrorist link.
An attack on this scale on the most popular of all Turkey's tourist areas is unprecedented in recent years and could have huge consequences for the country.
10:09 GMT - Images published by Turkey's Dogan news agency apparently show bodies on the ground.
The explosion was powerful enough to be heard in adjacent neighbourhoods, witnesses tell AFP. Police have cordoned off the area to passers-by and tourists and the nearby tram service has been halted.
10:11 GMT - "The explosion was so loud, the ground shook. There was a very heavy smell that burned my nose," a German tourist named Caroline tells AFP.
"I started running away with my daughter. We went into a nearby building and stayed there for half an hour. It was really scary."
10:12 GMT - Media reports say the blast took place at 0820 GMT around the Obelisk of Theodosius, a monument from ancient Egypt that was re-erected by the Roman emperor Theodosius and is one of the city's most eye-catching monuments.
10:16 GMT - TURKEY PM CONVENES EMERGENCY SECURITY MEETING AFTER ISTANBUL BLAST
10:23 GMT - Turkish Prime Minister Ahmet Davutoglu convenes an emergency security meeting of key ministers and officials after the suspected attack on Istanbul's tourist hub of Sultanahmet which left 10 people dead.
Those taking part in the meeting include the powerful Interior Minister Efkan Ala and spy chief Hakan Fidan, the Anatolia news agency says.
10:46 GMT - GERMANY WARNS NATIONALS TO AVOID TOURIST SITES IN ISTANBUL
10:54 GMT - Germany warns its citizens to avoid crowds and tourist sites in Istanbul.
"Travellers in Istanbul are strongly urged to avoid for now large groups of people in public places as well as tourist attractions and to stay abreast of the situation via these official travel advisories and the media," the foreign ministry says.
According to some media reports, German tourists are among the people wounded in the Sultanahmet explosion. The Istanbul governor's office says a total of 10 people have been killed and 15 wounded.
11:14 GMT - "I heard a very loud blast, then came the screams," a Turkish man who asked not to be named tells AFP.
"Then I saw a ball of fire, and started to run away. I saw about 10 people wounded, one of them was being helped by the tourists. I am 100 percent sure it wasn't just a bomb, but a suicide bomber," he adds.
11:18 GMT - The authorities have imposed a broadcast ban on reporting of the attack from Sultanahmet, prompting television channels to halt live broadcasting from the scene although factual commentaries continued.
11:19 GMT - The identities of those killed and wounded are not yet clear although unconfirmed reports say the injured include two Germans and one Norwegian tourist.
11:25 GMT - More from Germany's foreign ministry on the situation in Istanbul after today's blast:
The ministry warns on its website of possible "political tensions as well as violent clashes and terrorist attacks across the country", adding that tourists should avoid large demonstrations.
Officials tell AFP that crisis teams at the ministry in Berlin and the consulate in Istanbul are working to establish the facts after the blast.
11:34 GMT - ERDOGAN SAYS ISTANBUL ATTACK CAUSED BY SUICIDE BOMBER OF SYRIAN ORIGIN
11:40 GMT - Turkish President Recep Tayyip Erdogan says the attack on Istanbul's tourist heart was carried out by a suicide bomber of Syrian origin.
"I strongly condemn the terror attack which was carried out by a suicide bomber of Syrian origin," Erdogan says in a speech in Ankara in his first reaction to the blast.
12:01 GMT - More from Turkish President Recep Tayyip Erdogan's speech in Ankara:
"Unfortunately... there are fatalities, including locals and foreigners. This incident showed again we have to stand together in the face of terror."
12:03 GMT - Erdogan adds: "Turkey's determined position will not change. We don't make any difference between the names or abbreviations (of terror groups)."
"The first target of all the terror groups active in this region is Turkey. Because Turkey fights them all with the same determination."
Turkey has been on high alert after a series of attacks blamed on the Islamic State jihadist group including a double suicide bombing in the capital Ankara in October that left 103 people dead.
But Turkey is also cracking down on the outlawed Kurdistan Workers' Party (PKK), which Ankara and its Western allies classify as a terror group.
12:22 GMT - MAJORITY OF DEAD IN ISTANBUL SUICIDE BOMBING ARE FOREIGNERS: MINISTER
12:23 GMT - ISTANBUL BOMBER IDENTIFIED AS SYRIAN NATIONAL BORN IN 1988: MINISTER