Afghanistan's defense minister, who played a key role overseeing the rapid expansion of the country's army, stepped down on Tuesday days after receiving a no-confidence vote from parliament.

The resignation of Abdul Rahim Wardak, one of the members of President Hamid Karzai's cabinet who was trusted by Washington, leaves his key ministry without its longstanding leader at a time when Afghan troops are charged with taking over responsibility from international forces by the end of 2014.

Separately, a truck bomb rammed into the gate of a NATO base in eastern Afghanistan, seriously wounding several people, while a roadside explosion killed nine civilians riding in a bus near the Afghan capital. NATO also reported that three service members were killed during the past two days as fighting continued in the east and south where militants have their deepest roots.

Lawmakers on last Saturday passed no-confidence votes against Defense Minister Abdul Rahim Wardak and Interior Minister Bismullah Khan Mohammadi, faulting them for what they said was the government's weak response to cross-border attacks that Afghans blame on the Pakistani military.

The lawmakers, who asked why Afghanistan had not launched a military response, also quizzed the ministers about allegations of corruption within their ministries and alleged security lapses that led to recent assassinations of top officials.

Instead of replacing them as the parliament demanded, Karzai named Wardak and Mohammadi as acting ministers. Mohammadi remains acting interior minister, but Wardak, who is in his late 60s or early 70s, decided to step down.

"As an Afghan citizen, I believe in democracy and I respect their (the parliament's) decision," he said, adding that the Afghan people and history will judge his service to the nation.

Wardak, who served in the Afghan government through more than four decades of national turmoil, thanked Karzai for choosing him to lead the rehabilitation of the Afghan National Army, which has grown from around 50,000 to more than 195,000 under his watch, but remains plagued with corruption and unprofessionalism.

Before voting against him, parliamentarians twice confirmed Wardak as defense minister.

Wardak studied in the U.S. and speaks English fluently, and has been long backed by Washington and the NATO military coalition. The coalition declined to comment on Afghan politics but said the plan for Afghan soldiers and police to be in charge of security across the country by the end of 2014 remained on track.

He has been defense minister since late 2004, was deputy defense minister before that and held other positions in the Karzai administration.

In the 1980s, he was a well-known leader of mujahedeen fighters against the Soviet and Afghan communists.

As Wardak spoke, a third member of President Hamid Karzai's cabinet was defending his record in another part of the Afghan capital.

Afghan Finance Minister Omar Zakhilwal asked government prosecutors on Tuesday to investigate allegations against him of wrongdoing involving bank deposits and transfers. He vehemently denied the allegations and said an investigation would clear his name.

The government's anti-corruption unit is looking into sizable deposits that businesses and individuals made to Zakhilwal's bank accounts. The country's Tolo Television, which was first to report the probe last week, showed viewers copies of bank statements from 2007 to 2011 that Tolo said showed more than $1 million being transferred to Zakhilwal, some of which it said was later moved out of the country.

Zakhilwal, who was educated at Canadian universities, has said that the money in the accounts was earned from his work as a consultant for international institutions and as an author.

Zakhilwal asked government prosecutors to launch an independent and impartial investigation and release the results to the nation. In a letter to the attorney general, Zakhilwal said the allegations against him were "biased, false and insulting with a clear intention to damage my national and international reputation."

Meanwhile, violence continued across the country. The Taliban claimed responsibility for Tuesday's midmorning blast at a NATO base in Logar province, southeast of Kabul.

A suicide attacker, who has placed the explosives under a load of gravel, drove the pickup truck into a gate of the base near Logar's capital of Pul-i-Alam, provincial police chief Ghulam Sakhi Roogh Lawanay said. He said the truck belonged to a local contractor authorized to work at the base.

At least 11 Afghan civilians were wounded, he said.

NATO said the blast did not cause any significant damage to the base.

Earlier in the morning, a remote-controlled roadside bomb struck a bus travelling northwest of Kabul, killing at least nine passengers, police said. The militant who set off the device was spotted running away from the scene and was captured by local villagers in Paghman district of Kabul province.

The bomb was placed under a bridge and was detonated when the bus drove over the span around 7 a.m., said Mohammad Zahir, the criminal director for Kabul police. Broken glass and abandoned shoes of victims littered the road near the bus, which was flipped onto its side.

NATO said one of its service members was killed Monday by insurgents in the south and two others were killed on Tuesday - one in a roadside bombing in the south and the other in an insurgent attack in the east. No other information was released. So far this year, 271 U.S. and NATO troops have died in Afghanistan.