MUZAFFARABAD, Pakistan/NEW DELHI, May 7 (Reuters) - India attacked Pakistan and Pakistani Kashmir on Wednesday and Pakistan said it had shot down five Indian fighter jets in the worst fighting in more than two decades between the nuclear-armed enemies.

India said it struck nine Pakistani "terrorist infrastructure" sites, some of them linked to an attack by Islamist militants on Hindu tourists that killed 26 people in Indian Kashmir last month. Islamabad said six Pakistani locations were targeted, with eight people killed.

Indian forces attacked the headquarters of Islamist militant groups Jaish-e-Mohammed and Lashkar-e-Taiba, an Indian defence source told Reuters.

"India has demonstrated considerable restraint in selection of targets and method of execution," the Indian defence ministry said in a statement.

Pakistan said Indian missiles hit three sites and a military spokesperson told Reuters five Indian aircraft had been shot down, a claim not confirmed by India.

"All of these engagements have been done as a defensive measure," military spokesperson Ahmed Sharif Chaudhry said. "Pakistan remains a very responsible state. However, we will take all the steps necessary for defending the honour, integrity and sovereignty of Pakistan, at all cost."

Islamabad called the assault a "blatant act of war" and said it had informed the U.N. Security Council that Pakistan reserved the right to respond appropriately to Indian aggression.

The nuclear-armed South Asian neighbours also exchanged intense shelling and heavy gunfire across much of their de facto border in the Himalayan region of Kashmir, police and witnesses told Reuters.

India and Pakistan have fought two wars since 1947 over Muslim-majority Kashmir, which both sides claim in full and control in part.

Since a 2003 ceasefire, to which both countries recommitted in 2021, targeted strikes between the neighbours are extremely rare, especially Indian strikes on Pakistani areas outside Pakistani Kashmir.

But analysts said the risk of escalation is higher than in the recent past due to the severity of India's attack, which New Delhi called "Operation Sindoor".

U.S. President Donald Trump called the situation "a shame" and added, "I hope it ends quickly."

U.N. Secretary-General Antonio Guterres called for maximum military restraint from both countries, a spokesperson said.

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