JAMMU, India, July 2 (AP) - Thousands of Hindu worshippers began a tough pilgrimage Monday to an icy stalagmite worshipped as an incarnation of the god Shiva in a Himalayan cave in Kashmir, as authorities stepped up security to prevent attacks by Islamic guerrillas. Accompanied by doctors and soldiers, the first batch of 3,000 pilgrims, mostly saffron-clad Hindu hermits, left in a security convoy from a sports stadium on the journey to the Amarnath shrine in northern Kashmir. The pilgrims will be allowed to visit the shrine for a month. The state government has brought in 15,000 troops to provide security to Hindu devotees. Many are checking the route for land mines and booby traps. The pilgrims shouted religious slogans, chanted Hindu hymns and cheered as they boarded buses for the tourist resort of Pahalgam, their first stop. Many Hindu hermits clambered on top of buses, raising slogans in praise of Shiva, the Hindu god of destruction believed to live in the Himalayan mountains. In previous years, Islamic guerrillas have made public threats and carried out attacks on the pilgrims or accompanying security forces. Thirty-five pilgrims were killed last year. In shootouts between soldiers and suspected militants, 102 people were killed. Armed soldiers in bulletproof vests kept watch over the pilgrims from bunkers along the Jammu-Pahalgam highway where the buses passed. Pahalgam is the base camp for the pilgrimage and the last motorable point. Pilgrims will thereafter undertake an arduous trek of 45 kilometers (27 miles) to the deeply revered shrine, located in a cave. The Amarnath shrine is located at a height of 13,500 feet (4,110 meters), and houses an icy stalagmite worshipped as an incarnation of Shiva. Children and elderly pilgrims cover most of the trek on ponies and wooden palanquins. Policemen and paramilitary soldiers will be posted along the entire pilgrimage route, the state's police chief Ashok Kumar Suri said Sunday. Ambulances and oxygen cylinders will also be on standby. Volunteer agencies have set up free food stalls. An estimated 100,000 pilgrims are expected to make the pilgrimage this year in separate batches. It will conclude in the first week of August, with the main prayers scheduled for Aug. 4, a full moon night. The start of the Amarnath pilgrimage comes two weeks before a crucial summit between Prime Minister Atal Bihari Vajpayee and Gen. Pervez Musharraf of Pakistan, in which the Kashmir dispute will be discussed between the two leaders. Meanwhile violence continued in Kashmir. Four rebels were killed in separate gunbattles with security forces, which also left an army major and a soldier dead, a police statement said. India accuses Islamabad of arming, training and funding Pakistan-based Islamic guerrillas, who have sustained a violent 11-year campaign against Indian security forces in Kashmir. Pakistan says it backs them with ideology, not weapons. Most of the dozen militant groups operating in Kashmir are based in Pakistan. More than 30,000 people have been killed since the insurgency began in 1989.