A Belgian woman who converted to Islam after marrying a radical Muslim carried out a suicide attack in Baghdad earlier this month, say Belgian prosecutors.
Police searched houses in Brussels and other cities
Other European extremists are known to have travelled to Iraq to fight the US-led forces, but she is believed to be the first female European bomber.
On Wednesday, police detained 14 people in raids on the homes of people thought to have links with the unnamed woman.
Authorities said they wanted to break a network sending volunteers to Iraq.
Nine of the suspects are Belgian, three are Moroccan and two are Tunisian.
The federal prosecutor's office confirmed that a Belgian-born woman had carried out an attack in Baghdad on 9 November.
She is believed to have been born in Belgium and converted to Islam after marrying a Muslim radical. Her husband is reported to have been killed in Iraq in a separate incident.
The De Standaard newspaper said the woman's Belgian passport was found on her body after the attack on a US military convoy. She is reported to be the only victim of the attack.
Federal police director Glenn Audenaert told reporters that the Belgian authorities wanted "to dismantle this network, which we knew was on our territory and which aimed to send volunteers for the jihad to the battlefield".
"This is how she came into contact with the organisation which allowed her to become a fighter for jihad," said Mr Audenaert.
Earlier this year, French Interior Minister Nicolas Sarkozy said at least seven people from France have been killed in Iraq and elsewhere fighting for al-Qaeda.
Belgian authorities have also had to deal with other cases of Belgian-based Islamic extremism. Thirteen men are currently on trial accused of membership of a militant group that has been linked to bombings in Madrid and Casablanca.
Defence lawyers say the only evidence against some of them is that they knew men charged with serious crimes.
The men are accused of belonging to the Moroccan Islamic Combatant Group (GICM), accused by the US of aiming to establish an Islamic state in Morocco and supporting al-Qaeda's jihad against the West.