Pakistan on Thursday registered a formal protest against alleged violations of its airspace by Indian fighter jets last week, an incident which New Delhi [Images] has already denied.

India's Deputy High Commissioner Manpreet Vohra was handed over a note regarding the alleged airspace violations by Pakistan's Additional Secretary (South Asia) Aizaz Ahmad Chaudhry during a meeting at the Foreign Office on Friday morning, diplomatic sources said.

The note conveyed Pakistan's concerns about the incident and sought an explanation from India, they said.

The sources denied that Pakistan had issued a demarche in connection with two alleged airspace violations that occurred on December 13.

Pakistan has claimed that two Indian jets entered its airspace in the Pakistan-occupied Kashmir and Lahore [Images] sectors. Indian Air Force's spokesman Wing Commander Mahesh Upasani denied that any of its combat jets had intruded into Pakistani airspace.

Speaking a day later, President Asif Ali Zardari [Images] had sought to play down the incident by describing them as a 'technical incursion'. Zardari said such incidents occurred when fighter jets made turns while flying at heights of up to 50,000 feet.

The Pakistan Air Force spokesman had said Indian authorities had been contacted about the incident and he too described it as a 'technical incursion of a minor nature made by mistake'.

The war of words between India and Pakistan on the issue comes as their armed forces have girded up to a state of vigil along the borders with tensions between New Delhi and Islamabad [Images] mounting over the terror attacks in Mumbai, which has been blamed on Pakistan-based elements.