Three Israeli soldiers and an Egyptian policeman were killed in shootings along the southern border with Egypt on Saturday, militaries of the two sides said.
The Israeli army said two soldiers – a man and a woman – were shot dead near the Egyptian border, and the third during an exchange of fire with an assailant in the area of the Paran Regional Brigade.
“The assailant is an Egyptian policeman,” it said.
“An investigation is being conducted in full co-operation with the Egyptian army”
It added that soldiers were searching the area to “rule out the presence of any additional assailants”.
The Israeli army later identified the woman killed as Lia Ben Nun, 19. A non-commissioned officer was also lightly injured, it said.
A spokesman for Egypt's armed forces said that “a member of the security forces breached the border security barrier” while in pursuit of drug smugglers, leading to the death of three Israeli soldiers and injuries to two others.
The Egyptian security serviceman was killed in the exchange of fire, the spokesman’s statement said.
"The fatal incident at the Egyptian border during the Sabbath is serious and unusual and will be thoroughly investigated," Israel's Prime Minister Benjamin Netanyahu said.
Israeli Chief of General Staff Maj Gen Herzi Halevi and the commander of the Southern Command conducted an investigation and assessment of the situation at the site of the incident, the Israeli army said.
Hours before the deadly shooting, Israeli soldiers had foiled an attempted drug-smuggling operation at the border, seizing contraband estimated to be worth 1.5 million shekels ($400,000), a spokesman said.
The spokesman added that no link had been established between the drug seizure and the attack along the border.
Earlier in the day, Israel's Army Radio had reported that two Israeli soldiers were shot while forces were trying to thwart smuggling activity in the area.
Egypt was the first Arab country to make peace with Israel following the Camp David accords of 1978 and the border is largely peaceful, although drug smugglers have occasionally exchanged fire with Israeli troops.
There have been incidents in the recent past along Israel's border with Egypt.
In 2011, assailants who came from Sinai killed eight Israelis in a triple ambush north of Eilat. Pursuing Israeli forces killed seven attackers and five Egyptian police.
In 2012, three militants who infiltrated from Sinai were killed, as well as an Israeli soldier, in a clash along the border.
Two years later, two Israeli soldiers on patrol were wounded by unidentified men who fired an anti-tank weapon from the Sinai during a drug-smuggling attempt, according to the Israeli military.
And in 2015, rockets fired from Sinai hit southern Israel without causing any casualties. ISIS later claimed responsibility.