YAOUNDE : Cameroon security forces killed some 40 Boko Haram militants in clashes in the country's far north, state radio said on Sunday, shortly after the release of two Italian priests and a Canadian nun suspected to have been held by the Islamist group.A presidency source confirmed the clashes, which took place west of the town of Kousseri, in the region bordering Nigeria and Chad. Cameroon, which has been criticised by Nigeria for not doing enough to fight the Nigeria-based Boko Haram, deployed some 1,000 troops to the far north this week as it steps up the fight against the Islamist militants. Moreover, In Brussels, NATO spokeswoman Oana Lungescu said NATO defence ministers would on Tuesday review measures the alliance had taken given Russia's actions towards Ukraine.She said this could include "enhanced air patrols over the Baltic states, AWACS surveillance planes over Poland and Romania, more exercises, and an enhanced naval presence by NATO allies from the Baltic to the Black Sea." "Defence ministers will also discuss the longer-term implications of the crisis and consider a readiness action plan in preparation for the Wales summit in September," she added.In April Poland's defence minister said Russia's military intervention in Ukraine's Crimea peninsula made it vital that NATO station significant numbers of troops in eastern Europe and ignore any objections Russia might have. Russia says deployment of significant NATO forces close to Russia would violate the 1997 Founding Act, an agreement between Moscow and the alliance. Eastern European states are nervous about Russia after it annexed Ukraine's Crimea region and massed 40,000 troops on Ukraine's borders. NATO is trying to provide reassurance with temporary deployments of military forces and exercises.