* India says strike on militant camps in Pakistan preemptive
* Three hundred militants killed in attacks - India govt source
* Pakistan downplays air strikes, says no casualties
* Tensions have risen since Feb. 14 suicide bombing in Kashmir (Adds comments from India foreign secretary, Indian government source)
By Drazen Jorgic and Sanjeev Miglani
ISLAMABAD/NEW DELHI, Feb 26 (Reuters) - Indian jets conducted air strikes against a militant camp in Pakistani territory on Tuesday, India's foreign secretary said, and a Indian government source said 300 militants had been killed, but Pakistan denied there had been any casualties.
The airstrikes hit a training camp of Jaish-e-Mohammed (JeM), the group that claimed credit for a suicide car bomb attack killed at least 40 Indian paramilitary police in Kashmir on Feb. 14, ratcheting up tensions between the two nuclear armed neighbours.
The action was ordered as India said it had intelligence that Jaish was planning more attacks.
"In the face of imminent danger, a preemptive strike became absolutely necessary," Vijay Gokhale, India's top diplomat, told reporters.
"The existence of such training facilities, capable of training hundreds of jihadis could not have functioned without the knowledge of the Pakistani authorities," Gokhale said.
Pakistan denies harbouring JeM, a primarily anti-India group that forged ties with al Qaeda and has been on a UN terror list since 2001. In December 2001, Jaish fighters, along with members of another Pakistan-based militant group, Lashkar-e-Taiba, launched an attack on India's parliament, which almost resulted in the two countries coing to war for a fourth time.
Gokhale said "a very large number" of militants were killed in a strike on a training base in Balakot, a town in a remote valley in Pakistan's Khyber Pakhtunkhwa province, but did not provide a precise figure for the casualties.
The commander of the camp was Maulana Yusuf Azhar, a brother-in-law of JeM leader Masood Azhar, Gokhale said.
A senior Indian government source said that 300 militants had been killed in the strikes. But no details were provided.
Pakistan downplayed the severity of airstrike, saying its own warplanes had chased off the Indian aircraft, which had released their "payload" in a forested area, causing no casualties and no serious material damage.
"Indian aircrafts intruded from Muzaffarabad sector," Pakistani military spokesman Major General Asif Ghafoor said on Twitter early on Tuesday, referring to an area in the Pakistan-held part of Kashmir.
Ghafoor said "facing timely and effective response from Pakistan Air Force", the Indian aircraft "released payload in haste, while escaping, which fell near Balakot. No casualties or damage".
Saying that more information would be released, Ghafoor tweeted four pictures of the alleged site where Indian aircraft dropped a payload near Balakot, purportedly showing a bomb crater in a forest area but no serious damage.
Pakistani villagers in the area where the Indian jets struck said they heard four loud bangs in the early hours of Tuesday but reported only one person was wounded.
"We saw fallen trees and one damaged house, and four craters where the bombs had fallen," said Mohammad Ajmal, a 25-year-old who visited the site.
Pakistan Foreign Minister Shah Mahmood Qureshi said on Tuesday that "better sense" should prevail, warning India not to challenge Pakistan.
While Gokhale did not comment on the status of the camps, India's minister of state for agriculture, Gajendra Singh Shekhawat, said on Twitter on Tuesday they had been "completely destroyed".
Indian television networks reported the airstrikes took place at 3.30 am.
Mohammed Iqbal, a resident of Mendhar, on the Indian side of the Line of Control (LoC), told Reuters that he heard jets flying through the night.
Balakot is about 50 km (30 miles) from LoC, the ceasefire line that is the de facto border in Kashmir, a Himalayan region that has been the cause of two of the three wars India and Pakistan have fought since the end of British colonial rule in 1947.
Analysts have alleged Pakistani militants have their training camps in the area, although Pakistan has always denied the presence of any such camps.
Indian markets fell on Tuesday amid concerns over increased tensions with Pakistan. The rupee weakened to 71.16 per dollar compared with Monday's close of 70.9850.
The 10-year benchmark bond yield rose to 7.61 percent compared with 7.58 percent on Monday, while the broader NSE stock index declined 1.17 percent.
Shelling across the LoC has occurred frequently over the past few years but airspace violations by jets are extremely rare.
New Delhi said in 2016, following another large attack on Indian security forces in Kashmir, that its troops crossed the LoC to carry out a "surgical strike" on suspected militant camps in Pakistan Kashmir. Islamabad denied anything serious occurred.
Indian Prime Minister Narendra Modi, facing a tight election in the next couple of months, has vowed a strong response to the Feb. 14 attack, the deadliest single assault on Indian forces in 30 years of insurgency in Jammu & Kashmir, India's only Muslim-majority state.
Pakistani Prime Minister Imran Khan denied his country was involved and offered to help investigate the attack if any credible evidence was provided. (Additional reporting by Asif Shahzad, Fayaz Bukhari and Neha Dasgupta Writing by Alasdair Pal Editing by Michael Perry and Paul Tait)