Malian troops approached the remote northeastern town of Kidal on Sunday ahead of a mid-May deadline set by the government to wrest it from the control of Tuareg separatist rebels.
French forces which swept Islamist insurgents from the far north of Mali have allowed the MNLA rebels to run Kidal in recent months but Mali's government wants to reimpose its authority ahead of July presidential and legislative elections.
The votes are intended to seal Mali's democratic transition in the wake of a March 2012 coup triggered by a Tuareg uprising, after which al Qaeda-linked Islamists seized control of the northern two-thirds of the landlocked West African country.
A column of Malian troops left Gao, the largest city of northern Mali, for Kidal earlier this week. Defence Minister Yamoussa Camara told parliament this month that the problem of MNLA control over Kidal would be resolved by May 15.
The MNLA has rejected Bamako's calls for it to lay down its weapons, saying it would resist any Malian attempts to retake Kidal, but has said it is open to political negotiations with the government.
Military sources said the army column had passed a small town 90 km (55 miles) southwest of Kidal on the road from Gao.
"They have passed Anefis and are heading toward Kidal," said one source, who asked not to be identified because of the militarily sensitive nature of the information.
Another army source said a second column was heading for Menaka, a town in eastern Mali close to the Niger border which was taken by the MNLA and then the Islamists last year.
"There is still time for negotiation before any military action," said the second source.
Kidal residents confirmed that Chadian troops, who had been based there as part of their operations against Islamists in the Adrar des Ifoghas mountains, had redeployed further north to the town of Aguelhoc.
The government in Bamako has insisted it will stick to July's electoral timetable, under pressure from Paris, despite security concerns in many parts of northern Mali.
On Friday, two attacks by the MUJWA Islamist group killed the five suicide bombers and injured two soldiers in Menaka and Gossi, a town near Gao.
The U.N. Security Council has approved the creation of a 12,600-strong peacekeeping force in Mali starting from July 1. France has started to draw down its troops but will keep a 1,000-strong rapid reaction force in Mali to combat the Islamist threat.
Some observers have questioned whether the infrastructure to hold elections can be quickly put in place in northern Mali, where Islamists destroyed many official documents during their 10-months in power.
While Paris is keen to turn the page on the interim government of Dioncounda Traore, overshadowed by the former coup leaders, many observers warn that poorly organised elections could lead to lasting political recriminations and a continuing north-south rift in Mali.
Tuareg separatists demand greater autonomy for their region but they are mistrusted by many in the majority black African south, who blame them for provoking last year's Islamist takeover.
Mali's army has been accused by human rights groups of carrying out reprisals against light-skinned Arabs and Tuaregs - ethnic groups associated with the Islamists.