BEIRUT (Reuters) – Russian warplanes were said to have launched heavy strikes on the Islamic State-held city of Palmyra on Thursday in what may be a prelude to a Syrian government bid to recapture the historic site lost to the jihadist group last May.

Dozens of Islamic State fighters were killed or wounded in the strikes that followed similarly heavy air raids in the Palmyra area on Wednesday, the Syrian Observatory for Human Rights monitoring group reported.

The attacks add to the pressure on a group that is losing ground to a separate, U.S.-backed campaign by Syrian militia in the northeast, and whose military commander was declared probably dead by U.S. officials on Tuesday.

The group’s tactics in Syria appear to reflect the strains, as it turns to suicide missions seemingly aimed at causing maximum casualties rather than sustainable territorial gains.

Islamic State is not included in a cessation of hostilities agreement that has brought about a lull in the war raging in western Syria between rebels aiming to topple President Bashar al-Assad and the Syrian army backed by the Russian air force.

Military operations against Islamic State in central and eastern Syria are continuing as both Damascus and its allies on one hand, and the United States and its allies on the other, seek to degrade Islamic State’s self-declared “caliphate” that stretches into Iraq.

The Observatory said Russian war planes carried out 150 raids in the Palmyra area on Wednesday, followed by further attacks on Thursday. “If they take Tadmur (Palmyra) and Qarayatain, the regime would have taken back a big geographic area of Syria,” said Observatory Director Rami Abdulrahman.

The loss of Qaraytain and Palmyra and the surrounding desert would reduce Islamic State’s hold to about 20 percent of Syria.

Qarayatain is 60 miles southwest of Palmyra. After capturing Palmyra, Islamic State blew up some of its ancient monuments in what the U.N. cultural agency UNESCO called a war crime.

Islamic State however appears well-entrenched in Palmyra, and while recovering the city would be a big boost for Damascus, its priority may be elsewhere for now, including the border with Turkey where it has been fighting rebels despite the truce.

FINANCES UNDER STRAIN

The momentum has turned against Islamic State since its rapid advances two years ago following the capture of the Iraqi city of Mosul. Its finances are also under strain, with fighters’ pay cut by up to a half.

In what would be another major blow to Islamic State, U.S. officials said on Tuesday that its “minister of war”, Abu Omar al-Shishani, was likely killed in a U.S. air strike near the town of al-Shadadi in northeastern Syria.

The militant, also known as Omar the Chechen, had a reputation as a close military adviser to Islamic State leader Abu Bakr al-Baghdadi.

The Pentagon believes Shishani was sent to bolster Islamic State troops after they suffered setbacks at the hands of U.S.-allied militias including the Kurdish YPG.

The Observatory, which says it gathers its information from sources on all sides of the war, said on Thursday that Shishani was badly wounded but still alive and being treated somewhere in the group’s Syrian stronghold of Raqqa province.

Recent Islamic State attacks have included suicide car bombings in the government-held cities of Damascus and Homs, and a determined but ultimately unsuccessful effort to sever the government’s only land supply route to Aleppo.

Dozens of its fighters were also killed in a Feb. 27 attack on the YPG-held town of Tel Abyad at the Turkish border. A YPG official sent Reuters a list of the names of 72 IS fighters he said had been sent there on a suicide mission.

The official said Shishani’s death, if true, would not be that significant because Islamic State “is being broken by the YPG and Syria Democratic Forces with or without him”. “It doesn’t change the equation at all as far as we are concerned.”

(Additional reporting by Omar Fahmy in Cairo; editing by Giles Elgood)