BAMAKO, Sept 15 (Reuters) - Mali, Burkina Faso and Niger will introduce new biometric passports as part of their withdrawal from a West African bloc in favour of a new Sahel alliance after military leaders seized power in all three countries, Mali's leader said on Sunday.

The three junta-led Sahel neighbours jointly announced in January they would leave the 15-member Economic Community of West African States (ECOWAS), which has sought to persuade them to reconsider their decision.

Burkina Faso announced earlier this month that it was rolling out new passports without the ECOWAS logo.

"In the coming days, a new biometric passport of the AES (Alliance of Sahel States) will be put into circulation with the aim of harmonising travel documents in our common area and facilitating the mobility of our citizens throughout the world", Malian junta leader Assimi Goita announced on Sunday evening.

He spoke ahead of a meeting Monday between the three countries' foreign ministers on the anniversary of the decision to form their own alliance. Goita also said they were planning to launch a shared information channel "in order to promote a harmonious dissemination of information in our three states."

ECOWAS has warned that the three countries' withdrawal would undermine the freedom of movement and common market of the 400 million people living in the 49-year-old bloc.

Their departure comes as their armies battle groups linked to al Qaeda and Islamic State, whose insurgencies have destabilised the region over the past decade and threaten to spill over into coastal West African states.