* Islamists likely to be suspected in deadly bombing
* First attack near capital in two years
* Bus station littered with blood and body parts
* Several hundred onlookers roam site of explosion (Adds detail, context)
By Isaac Abrak and Felix Onuah
ABUJA, April 14 (Reuters) - A morning rush-hour bomb killed at least 35 people at a Nigerian bus station near the capital on Monday, raising concerns about the spread of an Islamist insurgency after the first such attack on Abuja for two years.
Suspicion fell on Boko Haram, though there was no immediate claim of responsibility from the Islamist group mainly active in the northeast. Five hours after the blast, officials had given no death toll. Reuters journalists counted at least 35 bodies.
Security experts suspected the explosion was inside a vehicle, said Air Commodore Charles Otegbade, director of search and rescue operations. He gave no further details.
Henry Onyebulem, head of the clinical department of Asokoro general hospital, said that 27 dead had been deposited in the mortuary, while 25 critically injured are being treated.
More were expected, he said.
"I was waiting to get on a bus when I heard a deafening explosion then saw smoke," said Mimi Daniels, who escaped from the blast near Nyanyan bridge, 8 km (5 miles) south of Abuja, with minor injuries to her arm.
"People were running around in panic."
Bloody remains lay strewn over the ground as security forces struggled to hold back a crowd of onlookers and fire crews hosed down a bus still holding the charred bodies of commuters.
"These are the remains of my friend," said a man, who gave his name as John, holding up a bloodied shirt. "His travel ticket with his name on was in the shirt pocket."
The attack underscored the vulnerability of Nigeria's federal capital, built in the 1980s in the geographic centre of the country to replace coastal Lagos as the seat of government for what is now Africa's biggest economy and top oil producer.
Boko Haram militants fighting for an Islamic state have largely been confined to the remote northeast. They have been particularly active there over the past few months and are increasingly targeting civilians they accuse of collaborating with the government or security forces.
Suspected Islamist militants killed at least 60 people in an attack on a village in northeast Nigeria late last week. Eight people were killed in a separate attack at a teacher training college.
"In some ways it's not a big surprise. The situation has been escalating. It should be part of the strategy to 'bring it home' what's happening elsewhere in the northeast," said Kole Shettima, director of the MacArthur Foundation's Africa office in Abuja. "It's a statement that they are still around and they can attack Abuja when they want, and instill fear."
The Islamists, who want to carve an Islamic state out of Nigeria, have in the past year mostly concentrated their onslaught in the northeast, where their insurgency started.
There had been no attacks near the capital since suicide car bombers targeted the offices of Nigerian newspaper This Day in Abuja and the northern city of Kaduna in April 2012.
Security forces at the time said that was because a Boko Haram cell in neighbouring Niger state had been broken up.
A Christmas Day bombing of a church in Madalla, on the outskirts of Abuja, killed 37 people in 2011, although the main suspect in that attack is now behind bars. Boko Haram also claimed responsibility for a bomb attack on the United Nations' Nigeria headquarters that killed 24 people on Aug. 26, 2011.
Boko Haram, which in the Hausa language of largely Muslim northern Nigeria means "Western education is sinful", is loosely modelled on the Taliban movement in Afghanistan, and has forged ties with al-Qaeda-linked militants in the Sahara. (Additional reporting by Camillus Eboh; Writing by Tim Cocks; Editing by Louise Ireland and Alastair Macdonald)