Five employees of the ministry of mines and petroleum were killed and 10 wounded in the bus attack, the officials said, adding that seven people were killed and more than 20 wounded in the second explosion.
Stakes are high for the talks which follow a week of US-Taliban negotiations with both sides eyeing a resolution to the bloody 18-year conflict.
The Taliban have steadfastly refused to discuss peace with Ghani, whom they consider a US stooge heading an illegitimate regime.
Now is the “right moment” for peace in Afghanistan, President Ashraf Ghani said on Wednesday as he once more called on the Taliban to negotiate with his government.
The rush-hour explosion sent a plume of smoke into the air above the Puli Mahmood Khan neighbourhood of the Afghan capital and shook buildings up to two kilometres (1.2 miles) away, with the media reporter saying he could hear gunshots after the blast.
Four people were killed at a Swedish Committee for Afghanistan (SCA) centre in Wardak province, west of Kabul, during a night raid by Afghan forces last week,
Afghanistan's World Cup campaign was plunged further into crisis on Wednesday as coach Phil Simmons promised to lift the lid on simmering tensions with chief selector Dawlat Ahmadzai.
Sri Lanka rallied with the ball to beat Afghanistan by 34 runs in a World Cup match in Cardiff on Tuesday. Afghanistan bowled well to dismiss the 1996 World Cup champions for just 201.
Afghanistan defeated Pakistan by three wickets in their World Cup warm-up match at Bristol County Ground on Friday. In reply to Pakistan’s 262 all out in 47.5 overs, Afghanistan scored 263 for seven wickets, reaching the target with two balls to spare.