Afghanistan accused Pakistan of killing at least 400 people in an airstrike on a drug rehabilitation hospital in Kabul late Monday, marking a dramatic escalation in cross-border clashes that have seen repeated exchanges of fire and airstrikes. Pakistan denied targeting any civilian site, calling the allegations baseless.

The airstrike hit the hospital at about 9 p.m. local time, destroying large sections of the 2,000-bed facility, according to Afghan Deputy Government Spokesperson Hamdullah Fitrat. He said the death toll had “so far” reached 400 people, while about 250 were reported injured. Local television stations posted footage showing security forces using flashlights to carry casualties as firefighters struggled to extinguish flames among the ruins.

The strike came hours after Afghan officials said the two sides exchanged fire along their common border, killing four people in Afghanistan, as the deadliest fighting between the neighbors in years entered its third week. Afghan government spokesperson Zabihullah Mujahid condemned the strike, accusing Pakistan of “targeting hospitals and civilian sites to perpetrate horrors” and calling it “a crime against humanity.”

Pakistan’s Information Minister Attaullah Tarar said in the early hours Tuesday that the Pakistani military had “carried out precision airstrikes” targeting military installations in Kabul and the eastern province of Nangarhar. He said “technical support infrastructure and ammunition storage facilities” at two locations in Kabul were destroyed, asserting that all targeting was done with precision only at infrastructure being used by the Afghan Taliban regime to support “terror proxies.”

The United Nations Security Council on Monday called on Afghanistan’s Taliban rulers to immediately step up efforts to combat terrorism, a move that came as Pakistan intensified its accusations that Kabul harbors militant groups. Pakistan accuses Afghanistan of providing safe haven to the Pakistani Taliban—designated a terrorist organization by the United States—as well as to outlawed Baloch separatist groups and other militants who frequently target Pakistani security forces and civilians. Kabul denies the charge.

The latest conflict began in late February after Afghanistan launched cross-border attacks in response to Pakistani airstrikes inside Afghanistan that Kabul said killed civilians. The clashes disrupted a ceasefire brokered by Qatar in October after earlier fighting killed dozens of soldiers, civilians, and suspected militants. Pakistan has declared it is in “open war” with Afghanistan, and the conflict has alarmed the international community, particularly as the area remains a presence for militant organizations including al-Qaida and the Islamic State group.

Pakistani President Asif Ali Zardari said Afghanistan’s Taliban administration crossed a “red line” by deploying drones that injured several civilians in Pakistan last week. In response, Pakistan’s air force over the weekend struck equipment storage sites and “technical support infrastructure” in Afghanistan’s southern Kandahar Province, saying it was being used for attacks inside Pakistan. Kabul said Pakistan hit two locations, including an empty security site and a drug rehabilitation center that sustained minor damage.

In Kabul, Afghanistan’s administrative Deputy Prime Minister Abdul Salam Hanafi said defending sovereignty is the duty of all citizens. Speaking during a meeting with political analysts and media figures, Hanafi expressed regret over civilian casualties in recent Pakistani attacks, saying the war was imposed on Afghanistan.