Tanks rolled and fighter jets roared above India's main ceremonial avenue in an annual Republic Day military parade on Tuesday, hours after Indian and Pakistani troops exchanged heavy fire in the disputed Kashmir region. Celebrations were held under heavy security across India after recent hijack warnings and a spike in separatist violence in Kashmir, as well as border skirmishes between India and Pakistan. The border firing began shortly after midnight, the latest in recent security flare-ups between the South Asia rivals that have added to tensions, heightened by the 2008 Mumbai attack. A spokesman for Indian border guards said Pakistani troops fired to provide cover to separatist militants trying to sneak into Indian Kashmir from the Pakistani side. But a Pakistani security official said Indian forces used automatic weapons and mortar bombs in “unprovoked firing” that hit Bijhwat village near the Pakistani city of Sialkot. “Our troops retaliated with full force, also using heavy weapons, which ended the Indian firing that lasted for about half an hour,” spokesman Nadeem Raza said. No casualties were reported. In New Delhi, thousands of police and soldiers lined the 8-km route of the military parade as chief guest South Korean President Lee Myung-bak joined his Indian counterpart Pratibha Patil in a bullet-proof stand for Republic Day celebrations. The day marks the adoption of a republican constitution after independence from Britain in 1947. In a ceremony showcasing the country's military strength, tanks and armored cars rolled by, fighter jets roared through a misty winter sky in a full fly-past and helicopters hovered overhead, showering the crowd of thousands with rose petals. Colorful floats from each of India's 29 states also wound their way along a fogged out Rajpath, or King's Path, past the VIP stand towards the ancient Red Fort in the old quarter. Ahead of the celebrations, India draped itself in a heavy security curtain amid hijack warnings and stepped up violence in Kashmir, which is claimed by both India and Pakistan, but is ruled by them in part and is at the core of their dispute. A protest strike called by the separatists on Tuesday hit life in Srinagar, Kashmir's summer capital, witnesses said. Last week, the Interior Ministry recommended extra airline security checks after intelligence warnings of a possible hijack attempt. The air force was also put on the highest alert after agencies warned of a possible air attack by Lashkar-e-Taiba.