KABUL -- The United Nations on Tuesday called for an immediate reduction of violence in Afghanistan, warning that civilian casualties at the hands of both the Taliban and Afghan security forces are on the increase. The UN mission also expressed concern about stepped-up attacks and brutality of the Islamic State group.

A horrific attack last week at a maternity hospital in the Afghan capital has not been claimed by any group, but the United States said it bears all the hallmarks of Afghanistan's IS affiliate -- targeting the country's minority Shiites in a neighbourhood of Kabul that IS militants have repeatedly attacked in the past.

The Taliban denied involvement in the maternity hospital attack, which killed 24 people, including two infants and several new mothers.

The UN report blamed the Taliban for killing or injuring a total of 208 civilians last month and also said that operations by Afghan forces in April had killed or injured 172 civilians. Civilians are often caught in the crossfire of the fighting and Afghan forces say they are targeting the insurgents, not civilians, in anti-militant operations.

Taliban spokesman Zabihullah Muhahed disputed the UN figures in a tweet and blamed "blind airstrikes and artillery fire by U.S. and internal forces" for the casualties.

"Parties have committed to finding a peaceful solution and should protect the lives of all Afghans and not jeopardize people's hope for an end to the war," said Deborah Lyons, the UN chief's special representative to Afghanistan.

She added that "intra-Afghan peace negotiations need to start as soon as possible."

The UN's call for an end to violence comes as Washington's special peace envoy, Zalmay Khalilzad, began another round of talks with the Taliban to press them to start talking to the newly reconciled Afghan political leadership in Kabul and implement an immediate reduction in violence, said the U.S. State Department.

Khalilzad, who is the architect of a U.S.-Taliban deal signed in February, has been trying to salvage the agreement and jump-start intra-Afghan negotiations between the Taliban and the Kabul government.

A power-sharing agreement on Sunday between President Ashraf Ghani and his rival, Abdullah Abdullah, ended months of wrangling and raised expectations that the next round of the U.S.-Taliban peace deal, which calls for negotiations between the Taliban and Afghan leaders, can start.

The Taliban have said a permanent ceasefire would be on the agenda but have been critical of repeated delays in the promised prisoner release, which is to be completed before talks begin.

The U.S. State Department statement said Khalilzad would meet with the Taliban in Qatar, where the insurgents maintain a political office, and would "press for steps necessary to commence intra-Afghan negotiations, including a significant reduction of violence."

Khalilzad will also visit Kabul. U.S. Secretary of State Mike Pompeo, who said in March that the U.S. would cut $1 billion in U.S. aid to Afghanistan unless Ghani and Andullah resolved their differences, has bemoaned the time lost to their bickering.

"The United States remains committed to supporting the desire of the Afghan people and the international community for a political settlement that ends the 40-year conflict and ensures Afghanistan never again serves as a platform for international terrorism," the State Department statement said.

The U.S.-Taliban deal provides for the withdrawal of U.S. and NATO troops, but only if the Taliban live up to their end to battle other militant groups, such as the Islamic State affiliate.

The increasingly brutal IS attacks seem to have given urgency to U.S. efforts to get the Taliban into a co-ordinated battle against the group.

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Gannon reported from Islamabad