On Tuesday evening, a previously unknown Kurdish group calling itself the Kurdistan Liberation Hawks claimed responsibility for the bomb attacks.
In a statement carried on the Mesopotamian News Agency, the group claimed the blasts were in retaliation for recent Turkish army operations against Kurdish separatists in eastern Turkey.
The news agency previously carried statements from the Kurdish Workers Party (PKK), which has been fighting for an independent Kurdish state in Turkey.
However, another group, the al-Qaida-linked Abu Hafs al-Masri Brigades, also claimed responsibility for the early morning attacks.
"The Abu Hafs Brigades have carried out the first of a series of operations that will be launched in the face of European states," the statement posted on a website said.
It said the attacks were ordered after "all European states rejected the truce offered by our shaikh", referring to al-Qaida chief Usama bin Ladin.
"The bitterness that Muslims are tasting in Iraq and Palestine will be tasted by everyone living in Europe, in Istanbul, Rome and the rest of the countries that are following the policy of the United States," the statement said.
"Our position is clear. People of Europe, you will not enjoy security as long as you remain in your ugly silence. If you do not remove your governments, which have accepted the slaughter of Muslims, you will hear a response that you will not like"
Abu Hafs Brigades
The website statement also warned of more attacks throughout Europe.
"Our position is clear. People of Europe, you will not enjoy security as long as you remain in your ugly silence. If you do not remove your governments, which have accepted the slaughter of Muslims, you will hear a response that you will not like."
The statement continued: "Europe's rallying behind the mediocre [US President] Bush will lead to an escalating war that will not end without a change in policy by European states towards Muslims and their rejection of the criminal American policies that keep targeting Muslims in Iraq, Palestine and Afghanistan and the rest of the Muslim states".
The entrance to one of the two
hotels damaged by the blasts
The group warned: "There will not be safety [in Europe] unless your governments withdraw from the land of Iraq".
But with Kurdish separatists announcing earlier this summer they would target Turkey's tourism sector, some said earlier on Tuesday the authorities should explore all possible angles in the case.
"The Kurdish PKK-Kongra-Gel recently restarted their war against the Turkish state," said Erdinc Ergenc of Turkey's leading news site, Hurriyetim, "so this makes you think first of all about them. It seems to have been an organised attack, too, as there were several bombings".
The first bomb exploded at the Pars Hotel in the city's Laleli district that has many of the city's smaller budget hotels. It killed two people - a Turkish citizen and an Iranian national.
The main Kurdish guerrilla group
recently ended a unilateral truce
This was followed by another bomb at the Holiday Hotel in the nearby Sultan Ahmet district, also known for its small hotels and for most of the city's historical attractions.
Then bombs exploded at a liquefied petroleum gas-filling station in the city's outskirts.
In total, 11 people were injured in the explosions.
"For the moment everything is pointing to a terrorist attack," Istanbul police chief Celalettin Cerrah said on Tuesday morning.
Interior Minister Abd Al-Kadir Aksu pointed to recent operations in the city against the PKK-Kongra-Gel, saying that a few days ago, police raids had uncovered a flat containing bomb-making equipment. Seven suspects had been arrested, with four still in detention.
"The Abu Hafs
carried out the first
of a series of operations that will be launched
in the face of
statement posted on Abu Hafs al-Masri Brigades website
In addition, just the day before the bombs, officials from Turkish intelligence had issued a warning that the group might be targeting Turkey's cities.
However, Aksu added that it was also too early to draw any conclusions and that "whether the blasts have a connection with each other is being investigated".
Many analysts point out that the PKK-Kongra-Gel is at once embroiled in a protracted struggle with the Turkish authorities and bitter factional feuds.
"The government has ended many of the restrictions on Kurdish cultural rights recently, but maybe some groups within the PKK have decided to continue using terrorism against the Turkish state while other factions are against this," said Nilufer Narli of Istanbul's Kadir Has University.
The government has recently lifted bans on the Kurdish language, while the courts have released - pending an October retrial - several leading jailed Kurdish politicians, including Nobel-prize nominee Leyla Zana.
If a PKK group is behind the attacks, it would represent a shift in the theatre of conflict, as up to now, most of the fighting between the PKK-Kongra-Gel and Turkish security forces - which had claimed about 30,000 lives up to a unilateral ceasefire in 1999 - has been in the rural southeast of the country.
The last major attack took place
in Istanbul in November 2003
The PKK-Kongra-Gel ended its unilateral ceasefire earlier this summer. The group said the Turkish authorities had failed to respond with a ceasefire of their own, or to calls for talks and for the release of PKK-Kongra-Gel leader, Abd Allah Ocalan.
He has been in a Turkish jail since he was captured by Turkish
special forces in Kenya in 1999.
Since the end of the ceasefire, there have been repeated battles between Turkish soldiers and PKK-Kongra-Gel fighters in the southeast, along with several bomb attacks on Turkish officials.
Since 1999 too, the group has been largely confined to an enclave over the border in northern Iraq.
Recently, Turkey had renewed calls on the US occupation forces there to take action against this base, but without result.
Regardless of who was behind Tuesday's attacks, they spell trouble for the tourism sector, which is a staple of Turkey's economy and took in $1.7bn in income for the country in the first three months of this year alone.