A Russian soldier who belonged to the crack Spetznaz elite combat unit died a "hero'' after directing an airstrike on himself when Islamic State (ISIS) fighters surrounded his position near Syria's Palmyra town, a representative at the Russian base in Syria said.

The special forces officer was reportedly on a one-man mission at Palmyra for a week "identifying crucial ISIS targets and passing exact coordinates for strikes with Russian planes."

"An officer of Russian special operations forces was killed near Palmyra while carrying out a special task to direct Russian airstrikes at Islamic State group targets," according to the unnamed Russian representative.

"The officer died as a hero, he drew fire onto himself after being located and surrounded by terrorists."

Moscow has been conducting airstrikes against ISIS since Sept. 30, 2015. Russia's Defence Ministry said it carried out 146 airstrikes on "terrorist targets'' in the Palmyra area between Wednesday and last Sunday.

The aerial bombings came a day after Syrian troops reportedly recaptured Palmyra.

Meanwhile, U.S. military said several senior ISIS leaders were killed in bombing raids last week, adding that the fatalities included ISIS finance officer Imam Abd-ar- Rahman Mustafa al-Qaduli.

Al-Qaduli had a $7-million bounty on his head. U.S. defence officials say his death would make it more difficult for ISIS to operate and pay its fighters, Mirrok UK reported.

"We are systematically eliminating ISIS's cabinet,'' said U.S. Defense Secretary Ash Carter, adding that the latest killing of ISIS thugs is a "double blow'' to the hard-line Islamist group.

U.S. Marine General Joseph Dunford, chairman of the Joint Chiefs of Staff, described the recent attacks as "indisputable new momenum in the fight against ISIS."

The U.S. raids came three days after ISIS suicide bombers killed 31 people in Brussels—the worst terrorist attack in Belgian history.

Syrian soldiers have retaken the desert city of Palmyra from ISIS forces, recapturing its old citadel on Friday, reports said. The citadel overlooks some of the most extensive ruins of the Roman empire.

The historic site used to welcome over 150,000 visitors each year before the Syrian Civil War began in 2011. It boasts art and architecture from 100AD along with Greco-Roman ruins, over 1,000 columns, an ancient Roman aqueduct and 500 tombs on the vast site, according to reports.

But when ISIS captured the city last year, many of its ancient ruins, including temples and shrines deemed as blasphemous symbols were deliberately destroyed.