Tamil Tigers have become known for their use of suicide bombers
The use of two bus attacks in one day is clearly designed to spread fear in Sri Lanka which has seen a series of increasingly frequent attacks targeting civilians on public transport in recent weeks.
Suburbs of both the capital, Colombo, and the central town of Kandy have been targeted - spreading the geographical net wide on the same day.
Powerful fragmentation mines are increasingly being used to target crowded buses and trains in the south of Sri Lanka.
The attacks tend to be in suburbs and primarily kill and injure civilians where once the rebels used mine explosions to attack army buses carrying soldiers or naval personnel in the east of the island.
During the 25 years of Sri Lanka's civil war, the Tamil Tiger rebels have frequently changed tactics as they have built up their fighting force and equipped it with multi-barrelled rocket launchers, mortars and artillery.
RECENT COLOMBO ATTACKS
6 June: 20 killed in bomb attack on bus in suburb of Moratuwa
4 June: 24 injured in blast targeting commuter train
26 May: Bomb attack at Dehiwela station kills eight
16 May: Nine killed in suicide bombing in city centre
25 April: 24 killed in bus blast in suburb of Piliyandala
3 Feb: 11 killed in suicide attack at main city train station
But the Tigers are best known for their use of suicide bombers - often multiple suicide bombers, male and female.
And they have been blamed for high-profile bombs blasts at major infrastructure sites like the international airport, the port, the central bank or five-star hotels - attacks which psychologically dented financial confidence in Sri Lanka and often damaged the country's tourism industry.
There is nothing to suggest the rebels could not strike at the heart of Colombo if they wanted but it seems they have deliberately decided to cause panic in the public transport system and disrupt civilian life.
Those who suffer are commuters - ordinary people who fear the journey to work and worry about how to take their children safely to school.
The mere rumour of a bomb which may turn out to be caused by the sound of something harmless will send anxious parents rushing to collect their children from school.
So why may the Tigers have changed tack when their senior military leaders previously questioned why the Palestinian militant groups used suicide bombers to kill Israeli civilians at bus stops instead of hitting at big economic targets?
The damaged bus at the scene of the explosion
Many believe the attacks in the south are conducted by the Tigers in revenge for what they say is a sharp increase in claymore mine attacks on civilians in rebel-controlled territory.
The government does not give journalists access to rebel territory so attacks and their casualty figures there are impossible to verify.
But the Tigers accuse the government of using guerrilla-style tactics against them - employing what are called "deep penetration units", or Tamil-speaking paramilitaries, to infiltrate rebel areas and kill civilians. The government denies this.
Although there are military battles on the frontline between rebel and government territory in the north, it appears the war has descended into small-scale violence targeting civilians on both sides.
Living on the edge
These are attacks which serve little strategic military or political purpose except increasing the general sense of insecurity.
Attacks have dented confidence and damaged the tourism industry
Neither side can hope to win the war like this nor can they hope to change things politically by making civilians suffer more than they already have in decades of conflict.
Those minority Tamils who live in Colombo say they cannot remember ever being as scared as they are now.
It does not matter if they are doctors or lawyers - they expect to be questioned and searched at numerous roadblocks and checkpoints.
After every bomb some Tamils in the nearby locality will be rounded up for questioning and houses searched.
The security forces normally look in particular for anyone from the north-east of the island but even Tamils born and brought up in the south say they are treated with equal suspicion now.
The majority Sinhala community is also on edge like never before - watching who gets on buses, reporting suspicious parcels and avoiding public transport if they can possibly afford it - preferring to pay to hire an expensive private van than risk their lives on a train or bus.
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