IS targets EU tourists in Istanbul attack

"International terror changes the places of its attacks but its goal is always the same - it is our free life in a free society," she added, saying terrorists "are enemies of all humanity, whether in Syria or Turkey, in France or Germany".

The German foreign ministry also called on German citizens to "avoid crowds in Istanbul and other big cities in Turkey.”

The attack was carried out next to the Blue Mosque, in the Sultanahmet area - one of the most visited places in Istanbul - by a suicide bomber.

"We have determined that the perpetrator of the attack is a foreigner who is a member of Daesh," said Turkish prime minister Ahmet Davutoglu, using the Arab name for the Islamic State (IS) group.

Turkish president Recep Tayyip Erdogan for his part said the terrorist was Syrian and blamed Kurdish groups.

"For us, there is no difference between the PKK, PYD, YPG, DHKP-C ... or whatever their abbreviation may be. One terrorist organisation is no different than the other," he added, referring to Turkish Kurd and Syrian Kurd groups.

Warnings

The Istanbul attack follows other terrorist attacks in Turkey in recent months, including one which killed 103 people in Ankara last October during an opposition rally.

The October massacre was designed to create political instability ahead of the 1 November general election. But Tuesday's attack is designed to hurt Turkey's economic and diplomatic interests.

According to Turkey's Hurriyet newspaper, Turkish intelligence warned police in December and in early January that tourists, diplomatic missions, Nato and other international organisations are IS targets.

On 4 January, Turkish intelligence also warned other countries, including Germany, France, and the Netherlands of the risk of attacks, mentioning 13 potential suicide bombers, according to Germany's Der Spiegel.

Germany takes Turkish warnings "very seriously,” a German official told Der Spiegel.

Turkish intelligence is also said to have issued warnings on the November Paris attacks.

'EU and Turkey united'

The Istanbul bombing happened shortly after a visit to Ankara by EU commissioner Frans Timmermans, for talks on implementation of an EU-Turkey plan to reduce migrant flows.

Turkey is home to 2 million Syrian refugees. The EU would like them to stay there instead of coming to Europe.

Turkey is also involved in the Syrian conflict.

It supports the Western coalition against IS, but is also involved in fighting Kurdish groups on both sides of the Turkey-Syria border.

"The EU and Turkey stand united against all forms of terrorism," EU diplomacy chief Federica Mogherini and EU enlargement commissioner Johannes Hahn said in a statement Tuesday.

“The fight against terrorism was recognised as a priority at the EU-Turkey Summit on 29 November 2015 and we must step up our efforts in this regard in full respect of our obligations under international law, including human rights and humanitarian laws," they said.