ISLAMABAD (Reuters) - Pakistan said on Sunday said incidents of its security forces being targeted in cross-border attacks from Afghanistan had risen significantly, and called on Taliban authorities to act against militants, a day after purported air strikes by Pakistan.

       The incident has increased already simmering tensions between the neighbours.

       Taliban authorities on Saturday summoned Pakistan's ambassador in Kabul on Saturday to protest against the strikes. A local Taliban official and residents said the strikes were carried out by Pakistani aircraft inside Afghan airspace.

       "In the last few days, incidents along Pak-Afghan border have significantly increased, wherein, Pakistani security forces are being targeted from across the border," Pakistan's foreign office said in a statement on Sunday.

       It added the attacks were being carried out "with impunity" and that Islamabad had repeatedly asked Afghan authorities to act to stop them, but to no avail.

       It said seven Pakistani soldiers were killed in the border area of North Waziristan on Thursday. North Waziristan borders the eastern Afghan province of Khost, where the strikes are said to have taken place on Friday.

       Taliban authorities say they have controlled cross-border attacks since taking over the country in August last year.

       Pakistan's foreign office did not confirm the strikes, nor addressed if they were carried out by aircraft, which would be the first time a military incursion is officially confirmed.

       Pakistan's embassy in Kabul denied it carried out air strikes.

       The United Nations Assistance Mission in Afghanistan (UNAMA) expressed concern on the incident.

       "UNAMA is deeply concerned by reports of civilian casualties, including women and children, as a result of airstrikes in Khost & Kunar provinces," the body said on Twitter, adding it was working to establish the facts and verify losses.

       There was no confirmation of the death toll. A local Taliban official in Khost claimed at least 36 people, including civilians, had been killed.

       The Taliban government spokesman released a strongly-worded statement warning Islamabad of "bad consequences" if there was a repeat.

       "The defeat of the United States eight months ago was a good lesson to aggressors who want to disrespect Afghanistan's territory and freedom," Zabihullah Mujahid said.

       (Reporting by Gibran Peshimam in Islamabad, Saud Mehsud in Dera Ismail Khan and Kabul newsroom)