Three rockets were fired into the city's fortified “Green Zone” early Saturday morning, where two of them exploded near the NATO compound housing U.S. military personnel and other foreign forces.

A few hours later, a suicide bomber attacked a busload of military cadets, killing 15 of them, by detonating explosives near the entrance gate of the Marshal Fahim Military Academy, about seven miles from the NATO complex. Four of the cadets were also injured, a Defense Ministry spokesman said.

The attacks on the NATO complex caused no injuries or damage to the compound, said Capt. Tom Gresback, a spokesman for the U.S.-led NATO effort.

The explosions just before 6 a.m. echoed through the city's Shash Darak neighborhood, where the Afghan Defense Ministry and some foreign embassies are also located. No culprits have been identified, officials said.

Both attacks came a day after a massive suicide bomb attack on a Shiite mosque on the southwestern fringes of Kabul killed 39 people and injured another 45.

A funeral was held the day after 72 Shiite Muslims were killed at mosques in Kabul. (Reuters)

This week has been among the deadliest in Afghanistan this year, with more than 150 people killed during suicide bomb attacks in various provinces. Most of those attacks targeted Afghan police or military facilities. Another suicide bomb attack on a Sunni mosque in the Ghowr province Friday killed 20 people.