US ending talks with Russia on Syrian crisis: Kerry

US Secretary of State John Kerry says Washington is on the verge of putting an end to Syria talks with Russia over the assault on Aleppo.

"I think we are on the verge of suspending the discussion because, you know, it's irrational in the context of the kind of bombing taking place, to be sitting there, trying to take things seriously," Kerry said on Thursday in Washington, DC.

"There is no notion or indication of seriousness of purpose with what is taking place right now," he told a conference.

He added that the US would have to seek other alternatives for a period of time, “barring some clear indication by the warring parties that they are prepared to consider how to approach this more effectively."

Kerry made the remarks a day after warning his Russian Foreign Minister Sergei Lavrov he would walk away from the talks unless Moscow and Damascus stop airstrikes on Aleppo.

In response, Moscow said it was outraged by what it called the intimidating tone of the US statement, saying it shows Washington supports terrorism.

Moscow also criticized the White House for having “a non-constructive stance” on Syria.

Kremlin spokesman Dmitry Peskov told reporters on Thursday that the Russia would go on with its war on terror and continue to support Syrian government forces.

Moscow and Washington agreed on a milestone deal on the Syrian crisis after some 13 hours of marathon talks in the Swiss city of Geneva on September 9. The truce went into effect at sunset on September 12.

The truce, however, collapsed a few days later after the Syrian government accused foreign-backed militants of repeatedly violating the cessation of hostilities.

Syria has been gripped by foreign-backed militancy since March 2011. Over the past few months, the Takfiri militants active in the Arab country have suffered major setbacks as the Syrian army has managed to liberate several areas.