Israel’s military says U.N. observers in Lebanon were wounded by a buried explosive device.

A buried explosive device was the source of a blast that injured U.N. military observers in Lebanon over the weekend as they were patrolling the border with Israel, Israel’s military said Wednesday.

Three observers and a Lebanese translator were wounded in the blast on Saturday morning near the town of Rmeish. Two senior Lebanese security officials, who spoke on the condition of anonymity, had attributed the blast to Israel, without providing evidence. The Israeli military denied striking in the area.

In a statement on social media, a spokesman for the Israel military, Avichay Adraee, said that the blast was caused “by an explosive previously installed there by Hezbollah.”

Hezbollah, the powerful Lebanese militia and political movement, did not immediately comment on the claim. Hezbollah, which is backed by Iran, and other militant groups have been trading fire with Israeli forces across the border for months.

The U.N. peacekeeping mission in Lebanon, UNIFIL, had not completed its investigation into the incident, Andrea Tenenti, a spokesman for the mission said, but a preliminary report showed that “the explosion was not caused by direct or indirect fire.” He did not provide further details.

UNIFIL said that the wounded peacekeepers were an Australian, a Norwegian and a Chilean.

The peacekeeping mission was established to observe Israel’s withdrawal from Lebanon in the late 1970s. Since the 2006 war between Israel and Hezbollah, it has monitored and reported on violations of the subsequent cross-border truce.

Euan Ward contributed reporting.