At least 20 troops from a Saudi-led Arab coalition, including Yemeni expatriates in shorts, landed Sunday in Yemen’s southern coastal city of Aden on a “reconnaissance” mission amid a fierce offensive by Shiite rebels and their allies there, Yemeni military officials said.

The objective of the landing, which Saudi officials declined to immediately comment on, was not clear. However, military and security officials repeatedly have said that a ground operation would follow a Saudi-led airstrike campaign after the military capabilities of the Houthi rebels and their allies had been sufficiently weakened.

The Yemeni military officials and witnesses reached in Aden said the black-clad and masked coalition troops landed in a central area between Aden’s neighborhood of al-Mansoura and the airport. They said helicopter gunships hovered above the landing area. […]