(CNN) A huge explosion ripped through the diplomatic quarter of Kabul Wednesday, killing dozens of people and blowing windows out of nearby buildings in one of the deadliest attacks in the Afghan capital in years.
The Taliban -- the most influential terrorist group in Afghanistan -- have denied any involvement in the attack, which has turned the spotlight back on the country's 16-year war. Here's what you need to know.
The bombing is significant because of its scale and location, but also its timing.
Firstly, the blast hit rush hour traffic, signaling that its intent was pure terrorism.
Second, we are only a few days into the Islamic holy month of Ramadan. Like the ISIS attack on an ice cream shop in Baghdad earlier this week, this sends an utterly uncompromising message that nothing is off limits.
The location -- close to so many embassies -- will likely have been chosen to target embassy employees and weaken international resolve to help Afghans. Such a large blast occurring in such a secure area shows the capability of the bomb-makers to build a device so large that even strong security can be of limited value.
The scale of this blast -- larger than those we have seen recently -- also creates the impression that the war is getting worse and that no one is safe. Shock and fear are what the attackers thrive on. It may also be a message to US forces, who recently dropped the "mother of all bombs" on ISIS in targets in Afghanistan.
Over the past six months, security has been deteriorating in many parts of the country. In Kunduz in the north, the Taliban have made gains as well as in Helmand province in the south. Their influence is spread across most of the country.
ISIS is stronger in the east and has come under sustained attack from Afghan and US forces recently, particularly in Nangarhar province bordering Pakistan, where two months ago, American commanders for the first time dropped the largest non-nuclear US bomb ever used.
There are currently more than 8,000 US troops in Afghanistan, along with 6,000 from NATO and allied countries. The US and NATO are currently considering a very modest troop increase -- possibly several thousand.
ISIS militants are estimated to number in the hundreds and possibly low thousands if sympathizers are included. There are significantly more Taliban fighters.
The Taliban are the biggest threat to the Afghan government because they are greater in number, better organized, have deeper roots and a stronger political structure, and have more influence in the country.
ISIS is smaller and in some places fights the Taliban for local dominance. The Taliban for the most part have tried to stop ISIS gaining a foothold in Afghanistan.
Afghan and NATO forces are fighting both the Taliban and ISIS. US forces recently have increased their targeting of ISIS, focusing on potential international terror threats inside Afghanistan, as well as the local fight.
The coalition troop surge that is being suggested is unlikely to make a big impact in the short term. At the peak of the US troop surge in 2009 and 2010, there were about 130,000 coalition troops inside Afghanistan. While gains were made in many places, the Afghan army was unable to sustain stability.
Confirmation of the exact number of troops was expected last week. The delay indicates wrangling over troop commitments and purpose of deployment, although the expectation was for forces to help train the Afghan army and bulk up its forces.
The Afghan army has suffered very high causalities: in last year alone more than 6,500 troops have been killed and many more wounded.
Personnel retention is a problem due to pay, loyalty and casualties. More training by NATO forces is unlikely to fix these long-term leeches on the Afghan forces' strength.