WASHINGTON — Russia has sharply increased the number of combat aircraft at an air base near Latakia, Syria, giving its forces a new ability to strike targets on the ground in the war-stricken country.

Over the weekend, Russia deployed a dozen Su-24 Fencer and a dozen Su-25 Frogfoot ground-attack planes, bringing to 28 the number of warplanes at the base, a senior United States official said on Monday. Until the weekend, the only combat planes there had been four Flanker air-to-air fighters.

The deployment of some of Russia’s most advanced ground attack planes and fighter jets as well as multiple air defense systems at the base near the ancestral home of President Bashar al-Assad appears to leave little doubt about Moscow’s goal to establish a military outpost in the Middle East. The planes are protected by at least two or possibly three SA-22 surface-to-air, antiaircraft systems, and unarmed Predator-like surveillance drones are being used to fly reconnaissance missions.

“With competent pilots and with an effective command and control process, the addition of these aircraft could prove very effective depending on the desired objectives for their use,” said David A. Deptula, a retired three-star Air Force general who planned the American air campaigns in 2001 in Afghanistan and in the 1991 Persian Gulf war.