Russia's Defence Ministry says its warplanes have struck targets around the ancient city of Palmyra in support of the Syrian army's offensive there.

The ministry said Russian warplanes hit 146 targets Sunday through Wednesday, killing 320 militants. It said in Thursday's statement that Russian jets also destroyed five tanks, six artillery systems, two ammunition depots and 15 vehicles.

Backed by Russian strikes, Syrian government forces reached Palmyra, which has been held by ISIS since May.

President Vladimir Putin last week ordered a pullout of some Russian warplanes from Syria, but said that strikes against ISIS and the al-Qaeda-linked Nusra Front will continue. Those groups have been excluded from a Russian- and U.S.-brokered ceasefire that began on Feb. 27 and has largely held.

Russian officer killed: reports

Russian news agencies are citing a military official as saying that a Russian officer has been killed in fighting near Palmyra.

The state news agencies Tass and RIA Novosti said an official at Russia's Hemeimeem air base in Syria reported the death on Thursday and said it occurred as the officer was directing air strikes near the settlement of Tadmor on positions of the Islamic State group.

The official, whose name was not given, said the officer was spotted by fighters and surrounded.

The date of the death was not specified.

Is the 'nightmare' over?

A Syrian government official says he hopes that the "nightmare" of Palmyra is over after reports emerged that the army has reached the historic town.

Maamoun Abdulkarim, who heads the Antiquities and Museums Department in Damascus, says he hopes the damage inflicted by ISIS militants on the town's archeological treasures will not be worse than initially thought.

Many of the Palmyra's Roman-era relics, including the 2,000-year-old Temple of Bel and the iconic Arch of Triumph, have been blown up by ISIS. The town, a UNESCO world heritage site, has been held by ISIS since May.

Abdulkarim said on Thursday that the battle for Palmyra is a "cultural battle for the entire world and everyone who believes in common human heritage."

ISIS has been losing ground in Syria and Iraq for months under a stepped-up campaign of U.S.-led and Russian airstrikes, as well as ground assaults by multiple forces in each country.

On Thursday, Syrian state TV broadcast footage of its reporter, embedded with the Syrian military, speaking live from the entrance of Palmyra and saying that as of midday, the fighting was concentrated near the famed archeological site on the southwestern edge of the town. Cracks of gunfire and explosions echoed as the reporter spoke.

The fall of Palmyra to ISIS militants last year had raised concerns worldwide, and the destruction the extremists subsequently embarked upon sparked alarm and made international headlines. It was also a big blow to the government of Syrian President Bashar Assad, whose forces pulled out with apparently little resistance.

By nightfall, intense fighting was still taking place on the outskirts. Turkey-based activist Osama al-Khatib, who is originally from Palmyra, denied that Syrian troops had entered the town, and said the video seen on Syrian state TV was taken about five kilometres from Palmyra.

Earlier in the day, Gov. Talal Barazi told The Associated Press from the nearby city of Homs that the Syrian army was clearing roads leading into the town of mines and explosives

"We might witness in the next 48 hours an overwhelming victory in Palmyra," Barazi said, adding that "the army is advancing in a precise and organized way to protect what is possible of monuments and archeological sites."

ISIS instructed residents to leave the town Wednesday, according to a Palmyra native who asked not to be named. The town was mostly empty Thursday, save for ISIS fighters who were reported to be mining homes ahead of the advancing army.

Many of those who left sought refuge in ISIS-controlled cities in the country's north and east, including Deir el-Zour, which is also being contested between the extremist group and government forces, according to opposition media activists.

Affectionately known as the "bride of the desert," Palmyra had attracted tens of thousands of tourists to Syria every year.

Mideast Syria Islamic State

Syrian government forces were reported to have entered the town of Palmyra on Thursday. (Ron Van Oers/UNESCO/Associated Press)

Besides blowing up priceless archeological treasures, ISIS demolished the town's infamous Tadmur prison, where thousands of Syrian government opponents had been imprisoned and tortured over the years.

The advance on Palmyra comes against the backdrop of Syrian peace talks underway in Geneva between representatives of the Damascus government and the Western-backed opposition. The talks, which have been boosted by a Russia-U.S.-brokered ceasefire that has mostly held since late February, were to adjourn on Thursday — without having achieved any apparent breakthroughs.

Iraq starts operation to retake Mosul

Meanwhile, in Iraq, government forces pushed ISIS fighters out of several villages outside the town of Makhmour, southeast of the ISIS-held city of Mosul — a move that Iraqi and coalition officials cast as the start of an operation to retake the strategic city.

Yet it also follows the death of a U.S. marine stationed at a small U.S outpost close to Makhmour military base.

U.S.-led coalition spokesman U.S. army Col. Steve Warren told reporters he believed ISIS was specifically targeting the U.S. outpost and that ISIS attacks on the base had increased in recent weeks as Iraqi troops built up there and a larger number of U.S. and coalition forces moved in.

Regarding plans for a Mosul offensive, Warren said in a telephone interview that an Iraqi military buildup was still underway in the area.

"We announced several months ago that we had begun shaping operations for the eventual liberation of Mosul," Warren said. Thursday's "smaller ground operation conducted by the Iraqis is part of those shaping operations."

At a congressional hearing on Tuesday, Defence Secretary Ash Carter gave no indication that the Iraqis were ready for a full-scale counteroffensive. He said Iraq had "begun the shaping and isolation phase of the operation to collapse ISIL's [another name for ISIS] control over Mosul."

Iraqi forces retook several villages on the outskirts of Makhmour early Thursday and hoisted the Iraqi flag there, according to the spokesman for the Joint Military Command, Brig.-Gen. Yahya Rasool.

While the territorial gain does little for an eventual assault on Mosul, which U.S. and Iraqi officials recently said would take many months, it could push the front line between Iraqi and ISIS forces away from the Makhmour base.

The small U.S. artillery outpost near Makhmour has expanded the number and combat exposure of American troops in the country as Iraqi security forces prepare for a counteroffensive to retake Mosul, which fell to ISIS during the militants' June 2014 onslaught that captured large swaths of northern and western Iraq and neighbouring Syria.