KABUL (Reuters) - A wave of attacks on Afghan army, police and U.S. special forces in Kabul on Friday killed at least 50 people and wounded hundreds, dimming hopes that the Taliban might be weakened by a leadership struggle after their longtime leader's death.

The bloodshed began with a truck bomb that exploded in a heavily populated district of the capital and ended with an hours-long battle at a base used by U.S. Special Forces. It became the deadliest day in Kabul for years.

The radical Islamist insurgents claimed responsibility for both the police academy attack and the battle at the U.S. Special Forces base, though not for the truck bomb.

The scale of the violence heightened obstacles to reviving the stalled peace process and conveyed a no-compromise message from the Taliban at a delicate time following last week's revelation of Mullah Mohammad Omar's death and an ongoing dispute over leadership of the radical Islamist insurgency.

"The question is, who is sending the message?" Thomas Ruttig of the Afghanistan Analysts Network said.

The number of casualties from Friday's attacks was expected to rise as details continued to emerge from the authorities.

On Saturday, NATO-led coalition forces confirmed that one international service member and eight Afghan contractors were killed in the attack on Camp Integrity, a base used by U.S. Special Forces near the main airport.

The blast outside the base was powerful enough to flatten offices inside, wounding occupants who were airlifted by helicopter to military hospitals during the night.

"There was a big explosion at the gate ...(The gunfire) sounded like it came from two different sides," said a Special Forces member who was wounded when his office collapsed.

The initial blast caused by a suicide car bomb at the gate was followed by other explosions and a firefight that lasted a couple of hours, he said.

Camp Integrity is run by U.S. security contractor Academi, which was known as Blackwater before being sold to investors. Academi did not immediately respond to requests for comment.

"The helicopters went on for hours... medevacing people out," a U.S. contractor at a camp nearby said.

Dozens Killed, Wounded At Police Academy

The Camp Integrity assault followed a suicide bombing at a police academy on Friday evening that killed and wounded over 40 people, the Afghan interior ministry said on Saturday. A police source said the final tally was higher -- 26 killed and 28 hurt.

"The bomber was wearing a police uniform and detonated his explosives among students who had just returned from a break," a police official said.

Taliban spokesman Zabihullah Mujahid said the insurgents launched both the police academy and Camp Integrity attacks, but he earlier refused to comment on Friday's early morning truck bomb that tore through buildings in central Kabul, killing and wounding over 250 people.

The Taliban, who were toppled from power by the U.S.-led military intervention in 2001, rarely admit to attacks that kill a high number of civilians.

Divisions have broken out within the Taliban high command following last week's appointment of Mullah Akhtar Mansour as new leader. Previously seen as open to reviving peace talks, the Taliban have since pledged to press on with the insurgency that has killed and wounded thousands this year.

Ruttig said that with the latest attacks in Kabul, Mansour could be sending a message of resolve to the militant rank and file as well as to the Afghan government.

On the other hand, Taliban factions opposing Mansour's leadership could be seeking to kill any hope of future talks by launching their own wave of violence.

"The hope of some people was that the death of Mullah Omar would put the Taliban in disarray and possibly weaken them," Ruttig said. "I think that was a little over-optimistic."

The coalition death at Camp Integrity marked the second of an international service member in Afghanistan this year after most foreign troops withdrew at the end of 2014. The service member's nationality was not released.

The conflict between the Western-backed government and the Taliban has intensified since the NATO combat mission ended last year, but Afghan security forces and civilians have borne the brunt of the violence.

There have been almost 5,000 civilian casualties in Afghanistan in the first half of the year, U.N. figures show.