Afghan President Hamid Karzai said Monday that the massive Taliban offensive in Kabul and three other provinces showed a "failure" by the intelligence services, and especially by NATO. 

In his first statement regarding the 18-hour siege of diplomatic and government enclaves, Karzai also said that Afghan security forces proved themselves capable of defending their country and providing security, Reuters reported. 

Thirty-six insurgents were killed during the brazen attacks that also claimed the lives of eight policemen and three civilians, Interior Minister Besmillah Mohammadi told The Associated Press.

Battles which broke out at midday on Sunday gripped the city's central districts through the night, with large explosions and gunfire lighting up alleys and streets. 

"The fact terrorists were able to enter Kabul and other provinces was an intelligence failure for us and especially for NATO," Karzai's office said in a statement, which also strongly condemned the attack. 

Black Hawks pound building
NBC News' Sohel Uddin reported that, after an intense assault at Afghanistan's parliament, the fighting ended at around 6:20 a.m. local time Monday (9:50 p.m. ET Sunday) with Afghan forces firing their weapons in the air in victory.

He said he had watched NATO Black Hawk helicopters and Afghan forces pound a building "in an effort to flush out the few remaining insurgents."

Fighting in Kabul ends after 18 hours of intense gunfire

Officials in Afghanistan and U.S. Ambassador Ryan Crocker said the attacks appeared to bear the hallmarks of the Haqqani network and a top Afghan security official said an attacker who was captured alive had confessed the attack was carried out by the militant group, Uddin reported.

The Haqqani network has ties to the Taliban and al-Qaida. 

Afghan and U.S. officials are trying to coax the Taliban — which is not as closely linked with al-Qaida as the Haqqanis — to negotiate a political resolution to the 10-year-old war.

Afghans march to protest violence against women

If the Haqqani faction of the insurgency is behind the recent attacks, it could be easier to sell the idea of making peace with the Taliban to skeptics who say it amounts to making a deal with the enemy. 

Slideshow: Afghanistan: Nation at a crossroads

Ahmad Jamshid / AP

More than ten years after the beginning of the war, Afghanistan faces external pressure to reform as well as ongoing internal conflicts.

Launch slideshow

Though the death toll was much lower than other attacks, the dramatic assault on multiple targets showed that militants are far from beaten and can still penetrate Afghan security — even in the heart of the capital — after 10 years of war.

The attack also underscored the security challenge facing government forces as U.S. and NATO troops draw down and prepare to leave by the end of 2014. 

Afghanistan gets veto power over NATO night raids

International forces have been working to build up the Afghan army and police — a goal threatened by a growing number of insider attacks this year. In the latest such attack, an Afghan soldier opened fire on Bulgarian troops at his base Monday. 

The soldier fired from a guard tower down on the Bulgarians at a joint base in Kandahar city, said Col. Mohammad Mohsin, a spokesman for the Afghan army in Kandahar. The Bulgarian troops fired back, killing the Afghan soldier, Mohsin said. He said the attacker was from northern Takhar province. 

NBC News' Sohel Uddin, Reuters and The Associated Press contributed to this report.