(CNN) Syrian President Bashar al-Assad insists his forces must continue "to clean" Aleppo, even as diplomats prepare for a weekend of meetings aimed at halting the bloodshed in rebel-held areas of the city.

A renewed Syrian army offensive against eastern Aleppo, supported by Russian air power, has claimed hundreds of civilian lives in recent days and prompted Western powers to accuse Assad and his backers of war crimes.

But Assad, in a Thursday interview conducted in English with Russian newspaper Komsomolskaya Pravda, said the Syrian government has no option but to press on with its offensive.

"... You have to clean. You have to keep cleaning this area and to push the terrorists to Turkey ... to go back to where they come from, or to kill them.

"There's no other option. But Aleppo is going to be a very important springboard to do this move," he said.

"It's going to be the springboard, as a big city, to move to other areas, to liberate other areas from the terrorists. This is the importance of Aleppo now."

His remarks come as the United States, Russia and regional powers such as Saudi Arabia, Turkey and Qatar prepare to meet Saturday in Lausanne, Switzerland, for talks on Syria.

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US Secretary of State John Kerry will then confer with "key regional and international partners" in London on Sunday for further talks on ending the violence in Syria and the resumption of humanitarian aid deliveries, the State Department said.

Russian Foreign Minister Sergey Lavrov told CNN this week that he hoped Saturday's discussion might "launch a serious dialogue on the basis of the principles contained in the Russian-American deal," the ceasefire agreement that collapsed last month.

But Russian state news agency Tass quoted Lavrov as saying Friday that he has "no special expectations" for Saturday's meeting.

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"We would like to work in a concrete way and to see first to what degree our partners are prepared to comply with UN Security Council resolutions," he said during a news conference in Yerevan, Armenia, according to Tass.

However, he said, Russia will propose "concrete moves" to implement past Security Council resolutions on Syria and the earlier approved Russian-American agreements. Lavrov said that Western partners weren't engaging in "reciprocal steps" to settle the Syrian crisis.

Earlier Friday, Tass reported that Russian President Vladimir Putin had signed a law ratifying an agreement to keep a Russian air task force at Syria's Hmeymim airfield, in Latakia province, "indefinitely."

Renewed bombardment kills scores

Shelling and airstrikes this week have killed dozens of civilians in Aleppo , most in the east.

At least 160 people have died in the besieged rebel-held neighborhoods of eastern Aleppo in three days of airstrikes that resumed Tuesday, an activist at Aleppo Media Center told CNN.

At least 81 people were killed in airstrikes Tuesday on the Bustan al-Qasr neighborhood and at least 45 a day later in al-Fardous neighborhood, the activist said.

At least 20 airstrikes also hit the eastern part of the city Friday, the activist told CNN, but the exact number of dead and wounded from these strikes is unclear.

The aerial assault had been scaled back for several days when Syria began a ground offensive to take back rebel-held parts of the city.

Aleppo has become a focal point in the 5-year Syrian civil war, which the United Nations said already had cost around 400,000 lives in an estimate earlier this year.

The anti-government factions fighting for Aleppo -- dubbed terrorists by Assad -- include one-time al Qaeda affiliate Jabhat Fateh al-Sham, previously known as al Nusra Front. But members of groups supported by the West, including Free Syrian Army fighters, are on the battlefield, too.

Mounting humanitarian crisis

The Syrian government -- backed by Russian warplanes -- has been pounding Aleppo with regular airstrikes.

Up to a quarter of a million people are trapped by the fighting in and around the city, where aid agencies say a mounting humanitarian crisis is worsening by the day.

The ongoing siege has prompted strong protests from a number of countries and groups accusing Syria and Russia of war crimes against eastern Aleppo's beleaguered population.

Ramzy Ezzeldin Ramzy, deputy special UN envoy for Syria, told reporters Thursday that the situation in eastern Aleppo was dire, with hundreds of people, including children, in urgent need of medical evacuation.

Schoolchildren killed

There have also been deaths from shelling in government-held areas of Aleppo this week. The UN children's agency, UNICEF, said a mortar attack killed four children and injured three others on their way to school in the west of the city.

Earlier in the week, five children were killed when a school in a regime-held area of the southern city of Daraa was hit, according to state media and a UK-based monitoring group.

"In Syria, even going to school is dangerous," said Hanaa Singer, UNICEF representative in the country.

"In the city of Aleppo, daily indiscriminate attacks on populated areas kill and injure scores of children. Those who survive are witnessing gruesome violence that no child should ever see, leaving them with lifelong physical and psychological scars.

"Nothing justifies killing children."

Last week Kerry said Russian and Syrian military strikes against civilians and medical facilities in eastern Aleppo should be investigated as war crimes.

"Russia and the (Syrian) regime owe the world more than an explanation about why they keep hitting hospitals and medical facilities and children and women," Kerry said.

French President François Hollande and British Foreign Secretary Boris Johnson have also called for an International Criminal Court investigation into possible war crimes by Russia and Syria.