Six injured were received after the explosion in Kabul on Tuesday night, the capital's emergency hospital tweeted.
Official sources said it was a car bomb that exploded near Defense Minister Bismillah Mohammadi's residence in central Kabul.
No group immediately said they were behind the attack.
Indiscriminate shooting
The details of 40 killed and more than 100 injured in Lashkar Gah came in a tweet from the UN mission UNAMA earlier in the day.
It is the Taliban's attacks on the ground and government airstrikes that cause the most damage, UNAMA writes, expressing deep concern at the "indiscriminate firing" and occupation of health care facilities and ordinary people's homes.
Lashkar Gah with 200,000 inhabitants is the capital of Helmand Province.
The Taliban already control large parts of the countryside but have recently attacked major cities.
"Please leave!"
The government army is now asking the townspeople to leave Lashkar Gah immediately.
"Please leave as soon as possible so that we can begin our operation," General Sami Sadat urged via news media.
- I know that it is very difficult for you to leave your homes - it is difficult for us too - but please forgive us if you are forcibly relocated for a few days, he continued.
The Taliban have captured most local radio and television stations in recent days.
Officials killed
In Herat in northern Afghanistan, government forces forced the Taliban to withdraw from their latest offensive.
The government army says it has repulsed attacks on the airport, which is vital for supplies to Herat.
The Afghan Independent Human Rights Commission says the Taliban carried out revenge killings in the town of Spin Boldak near the Pakistani border, leaving at least 40 dead.
"The Taliban hunted down and identified current and former government officials and killed these people, who were not involved in any fighting at all," the group wrote.