Tripoli. Libya’s defence minister has resigned, calling a siege of government ministries by armed groups an "assault” on democracy.The resignation of Mohammed Mahmoud al-Bargati comes as gunmen in Libya’s capital Tripoli kept up their siege of ministries on Tuesday despite parliament’s adoption of a law to purge Gaddafi-era officials from their posts, which was supposed to appease the protesters.Some are demanding the government’s resignation."I will never be able to accept that politics [can] be practiced by the power of weapons ... This is an assault against the democracy I have sworn to protect,” Bargati said.He is the first cabinet minister to quit in a crisis over the siege.Gaddafi-era lawOn Sunday, Libya’s parliament voted to ban anyone who held a senior position during Muammar Gaddafi’s 42-year rule from government, a move which could also unseat the prime minister and other top officials regardless of their part in toppling the dictator.Politicians debated the draft law for months, but the issue came to a head this week when heavily armed groups took control of two ministries and stormed other institutions including the state broadcaster.The decision to hold the vote under duress could embolden the armed groups to use force again to assert their will over parliament.Members of parliament in Libya, plagued by armed disorder since Gaddafi’s demise, say the new legislation could be applied to around 40 of 200 deputies and could also unseat the prime minister, who some protesters demand should quit immediately.On Monday a spokesman for parliament conceded that the siege of the ministries was out of the government’s hands and that it would be up to the militiamen now to leave as promised.