LAGOS, Nigeria — Militants struck near the heart of the Nigerian state early Monday, bombing a bus station in the capital, Abuja, just miles from the seat of government in one of the worst attacks in years in the country’s struggle with insurgents.

At least 71 people were killed in a blast that ripped through dozens of vans and coaches, leaving a grim spectacle of dead and wounded. Top Nigerian officials, whose offices are a short distance away, immediately attributed the bombing to the Islamist group they have been battling for years, Boko Haram.

If that turns out to be the case — and the group itself rarely acknowledges its actions — Monday’s bombing would represent a significant amplification of Boko Haram’s bloody campaign to undermine the Nigerian state. Over the last two years, it has largely confined its attacks to remote areas of the country’s northeast, killing scores of civilians in the region’s towns and villages. On Sunday, more than 60 people were killed in an assault by the group near the border with Cameroon.