DRAS, India (AP) -- Indian air force jets and helicopters fired on suspected guerrillas in the disputed Kashmir province today, marking the most serious escalation of fighting in the region since India and Pakistan tested nuclear weapons last year. Pakistan charged that Indian aircraft bombed its territory in the raids today and an army spokesman said the country is ready for ``all eventualities.'' ``We think it is a very grave escalation and Pakistan armed forces reserves the right to respond,'' said Brigadier Rashid Quereshi, a military spokesman told The Associated Press. India said the attacks occurred solely on its own territory and that they were aimed at what it called Afghan mercenaries supported by Pakistani forces. The forces had moved into the Indian-controlled Himalayan region earlier this month and posed a threat to Indian supply lines in the Himalayan state, Indian officials said. ``This is the start of operations and they will continue until our defense forces reoccupy our territories. Any escalation of this conflict will be entirely the responsibility of Pakistan,'' the Defense Ministry said in a statement in New Delhi. Pakistani Foreign Minister Sartaj Aziz said that Pakistan knew nothing about the infiltrators. ``No one knows where they come from and who they are,'' he said. Quereshi said the army rejected Indian claims. He said the Pakistan army suspects India wants to occupy Pakistan territory in that area. India and Pakistan have fought two of their three wars over Kashmir, which is divided between them by a U.N-monitored cease-fire line. More than 15,000 people have been killed in fighting between rebels and security forces in Indian-held Kashmir in the last 10 years. Pakistan and India, which were partitioned when they gained independence from Britain in 1947, tested nuclear weapons in May 1998, prompting fears of a nuclear arms race in the subcontinent. Both countries claim all of Kashmir. India accuses Pakistan of sending militants across the border. A Pakistani army spokesman said the Indian allegations that elite troops were aiding militants was ``complete rubbish.'' Indian Maj. Gen. Joginder Jaswant Singh told reporters in New Delhi that the infiltrators have taken up positions four miles inside India in the Dras, Batalik, Kaksar and Mashkok mountains of northern Kashmir. Intelligence reports, backed by photos taken by Indian satellites, showed at least 600 infiltrators, Singh said. The reports also said they have anti-aircraft missiles, radar, snowmobiles and sophisticated communications equipment. The air force joined the operation because the infiltrators had occupied positions at altitudes of up to 16,000 feet, said Air Commodore Subash Bhojwani, director of offensive operations. In Dras, 100 miles from the state capital of Srinagar, Indian army officers said the target of today's attack was some 70 infiltrators who had entrenched themselves on the slopes of the snowcapped hills, looking down at Indian army convoys, 2,700 feet below. Their command of the heights handicapped Indian soldiers trying to evict them, officers told The Associated Press. Army officers in the area said the infiltrators must have taken months to occupy the posts. They said Indian forces could take three to six months to clear them. The attacks were carried out within Indian-occupied regions, Indian Brig. Mohan Bhandari said. Troops were expected to take over the intruders' positions once they retreat, officials said. The exchange of mortar and heavy artillery fire in the Kargil and Dras regions has left at least 160 people dead, Bhandari said. Thousands of residents of the region have fled to safe villages along the Suru River. The attack came a day after Prime Minister Atal Bihari Vajpayee said all steps -- including airstrikes -- would be taken to push back the infiltrators. Vajpayee said he warned his Pakistani counterpart, Nawaz Sharif, to withdraw the intruders in a telephone conversation Monday. -=-=- 