BAMIYAN, Afghanistan — Taliban insurgents mounted their most serious attacks in six years of fighting in Afghanistan over the last two days, including a coordinated assault by at least 10 suicide bombers against one of the largest American military bases in the country, and another by about 100 insurgents who killed 10 elite French paratroopers.

The attack on the French, in a district near Kabul, added to the sense of siege around the capital and was the deadliest single loss for foreign troops in a ground battle since the United States-led invasion chased the Taliban from power in 2001.

Taken together, the attacks were part of a sharp escalation in fighting as insurgents have seized a window of opportunity to press their campaign this summer — taking advantage of a wavering NATO commitment, an outgoing American administration, a flailing Afghan government and a Pakistani government in deep disarray that has given the militants freer rein across the border.

As a result, this year is on pace to be the deadliest in the Afghan war so far, as the insurgent attacks show rising zeal and sophistication. The insurgents are employing not only a growing number of suicide and roadside bombs, but are also waging increasingly well-organized and complex operations using multiple attackers with different types of weapons, NATO officials say.