Nato says it is restricting operations with Afghan troops following a string of deadly attacks on its personnel by rogue Afghan security forces.Only large operations will now be conducted jointly, with joint patrols evaluated on a case-by-case basis.This is a major step back for Nato’s strategy, says the BBC’s Quentin Sommerville in Kabul. It comes as a suicide bomber targeted a bus carrying foreigners in the capital, killing 12 people on Tuesday morning.The attack happened on a major road leading to the international airport and reports suggest those on board worked at the airport.Afghan insurgent group Hezb-e-Islami has claimed responsibility for the blast, which it says was in response to a recent anti-Islam video. Meanwhile Nato-led Isaf forces said they had arrested a Taliban leader and two insurgents they said were involved in an attack on the sprawling Camp Bastion in southern Helmand province.They said the leader was suspected of "providing support” to the militants who staged the audacious assault, killing two US marines and destroying six Harrier fighter jets.Rogue ‘surge’ The joint command of Nato-led Isaf international forces also cited "events outside of and inside Afghanistan” related to the film as part of the reason for its restrictions on joint operations. Afghanistan has seen days of protests over the video, some violent. Those, along with the surge in so-called "green-on-blue” attacks, had prompted the new restrictions, Isaf said.