Nairobi - Thirteen people have been killed in four attacks in Kenya during week-long celebrations to mark the country's 50th anniversary of independence, including the first attack on tourists in two years.
No one has claimed responsibility for the attacks - the most recent of which was an explosion on a Nairobi bus that killed four people Saturday - and there have been no arrests.
Kenya has been the target of sustained attacks since the army sent troops into neighbouring Somalia to fight the country's al-Qaeda-linked Shebaab insurgents in October 2011.
Eastern Kenya, along the 700km border with Somalia, has been particularly hard hit.
Experts are reluctant to draw any link between the armed conflict with the Shebaab and the latest series of attacks. One Western observer said that, as yet, there was "no evidence" to link the attacks.
Late on Friday, one person was killed and three injured in a double explosion at a market in the town of Wajir, some 100km from the Somali border.
On Tuesday, eight people were killed, including five policemen, in the Garissa region some 20km from the Somali frontier after their vehicle was attacked in an apparent ambush.
Another policeman is missing following the attack.
And Saturday's bus attack blew the vehicle apart, turning it into a mangled metal skeleton and sending shrapnel flying through the air. Four people died and 36 were wounded.
There was also a rare attack on tourists during the week in the popular tourist location of Mombasa, a predominantly Muslim city.
A grenade thrown at a minibus transporting British tourists hit a window, but did not explode. It was the first attack on tourists since 2011.
The British tourists were en route to the famous Masai Mara safari park.
In September 2011, British tourist David Tebbutt was killed as he fought kidnappers in a luxury tourist village on the Kenyan coast, not far from Somalia.
His wife, Judith, was captured and taken to Somalia, where she was freed after six months of captivity.
In the same year, a Frenchwoman living in Kenya, Marie Dedieu, was kidnapped by Somali gunmen from her beachfront home in Lamu, in the south-east of the country, and subsequently died.
"Mombasa has been targeted, but it is true that this attack against tourists is a novelty," the Western observer noted.
He said it was "very different" from the recent Westgate shopping mall terror attack, which left 72 dead.
That attack, in mid-September, was even deadlier than the bombing of the US Embassy in Kenya in 1998, which left 67 dead.
Many attacks remain unclaimed, though the finger of suspicion is often pointed at jihadists.
However, the authorities in the border regions and several other areas of Kenya know there are sometimes serious conflicts between tribes caused by issues such as access to water or grazing land, which can be fuelled by local politicians.
These conflicts, especially in areas where there is deadly weaponry, regularly escalate.