Afghanistan's army on Tuesday warned the residents of the besieged southwestern city of Lashkar Gah to evacuate ahead of a major offensive against Taliban militants.  Since foreign forces began the last stage of their withdrawal in early May, the Taliban seized control of much of rural Afghanistan.  The United Nations on Tuesday said at least 40 civilians were killed in the last 24 hours as fighting raged in Lashkar Gah. General Sami Sadat of the Afghan army told Lashkar Gah residents to leave the town as soon as they could. "Please leave as soon as possible so that we can start our operation," he said in a message to the city of 200,000. "I know it is very difficult for you to leave your houses — it is hard for us too — but if you are displaced for a few days, please forgive us," he added. "We are fighting the Taliban wherever they are. We will fight them, and ... we will not leave a single Taliban alive." Officials reported that the Taliban had seized nine out of 10 districts in Lashkar Gah, as well as more than a dozen local radio and TV stations in the city, leaving only one pro-Taliban channel. "Fighting was intense this morning," Sefatullah, director of Sukon radio in the city, was quoted as saying by the AFP news agency. US and Afghan air force planes hit Taliban positions, Sefatullah said, adding that the fighting was near Lashkar Gah's prison and a building housing police and intelligence headquarters.  The US had intensified airstrikes against the Taliban across Afghanistan in recent days.   Fighting has also been ongoing for days in the Kandahar province and in the western part of the city of Herat, in the west. DPA news agency reported, citing a hospital official, that at least 24 people died and nearly 200 were wounded in Herat in the past six days. Dozens of people were also reportedly killed in Kandahar and Helmand, the province of which Lashkar Gah is the capital.  A powerful blast rocked the Afghan capital, Kabul, on Tuesday evening, international media reported, but no details on the extent of damage were immediately available. A second explosion shook the city less than two hours later. The first explosion happened near a market square where there are government buildings, including the presidential palace, as well as foreign embassies and offices of international media and aid agencies. Media also reported gunfire at the home of the Afghan defense minister following the explosion. The minister, however, was reportedly not home at the time of the blast.  fb/sms (AFP, AP, LUSA, dpa) 