ANKARA: A suicide bomber who killed 10 German tourists in Istanbul entered Turkey as a refugee and his movements were not monitored as he was not on any watch lists, Turkish Prime Minister Ahmet Davutoglu said on Wednesday.

Asked whether Turkey planned air strikes against Islamic State in response to the bombing, Davutoglu said Turkey would act at a time and in a manner that it saw fit.

He said Russia's entry into the Syrian civil war had become a barrier to Turkish air strikes against Islamic State, and that the Russian air force appeared to be protecting the radical militants.

Related: German tourists among 10 killed in Istanbul suicide attack

The impact of Tuesday's attack, while not as deadly as two others last year, was particularly far-reaching because it struck at Turkey's $30 billion tourism industry, which has already suffered from a steep decline in Russian visitors since Turkey shot down a Russian warplane near the Syrian border in November.

The attack, which also wounded 15 other people — including Germans, a Norwegian man and a Peruvian woman — was the latest in a string of attacks by extremists targeting Westerners.

On Wednesday, Davutoglu, German Interior Minister Thomas de Maiziere and other Turkish officials visited the site of the blast and placed carnations there.

Germany sent a team of investigators to Istanbul on Wednesday from its Federal Criminal Police Office, which is comparable to the FBI, to support Turkish authorities investigating the attack.

Germany's Foreign Ministry said the number of dead Germans in Tuesday's explosion had risen to 10, but de Maiziere said there was no sign that Germans were specifically targeted.

"According to the investigations so far, there are no indications that the attack was directed specifically against Germans, so there can't be any connection to our contribution to the fight against international terrorism," de Maiziere said.