AMMAN, Jordan — Jordan’s security forces say the military has arrested four unarmed Syrian soldiers found in the zone between the two countries’ borders.

A security spokesman said the men were arrested on Monday and are being interrogated. He spoke on condition of anonymity because he is not permitted to make press statements

It was unclear whether the soldiers were trying to enter Jordan or were attempting to return to Syria.

The security spokesman could not provide further details as the probe is under way.

More than 1,000 senior Syrian army and police officers have defected to Jordan during the 21-month conflict.

Jordanian civilians living near the border with Syria reported heavy clashes between the Jordanian and Syrian armies late Saturday night, during which the Syrian army allegedly crossed the border and used attack helicopters.

One Syrian shell landed near a mosque in Ramtha, Qatari news channel Al-Jazeera reported on Sunday, causing Jordanian tanks stationed at the border to return fire towards Syria. Al-Jazeera reported a state of panic among Jordanian residents of the border area, some of whom left their homes after the shelling shattered their windows.

A Jordanian soldier was killed at the border on October 22 while trying to prevent militants from infiltrating into Syria. In August, a Jordanian soldier was injured while assisting Syrian refugees fleeing the regime to enter Jordan.