President Vladimir Putin intends to keep fighting in Ukraine until the West engages on his terms for peace, unfazed by Donald Trump's threats of tougher sanctions, and his territorial demands may widen as Russian forces advance, three sources close to the Kremlin said, Reuters reported.

Putin, who ordered Russian troops into Ukraine in February 2022 after eight years of fighting in country's east between Russian-backed separatists and Ukrainian troops, believes Russia's economy and its military are strong enough to weather any additional Western measures, the sources said.

Trump on Monday expressed frustration with Putin's refusal to agree a ceasefire and announced a wave of weapons supplies to Ukraine, including Patriot surface-to-air missile systems. He also threatened further sanctions on Russia unless a peace deal was reached within 50 days.

The three Russian sources, familiar with top-level Kremlin thinking, said Putin will not stop the war under pressure from the West and believes Russia - which has survived the toughest sanctions imposed by the West- can endure further economic hardship, including threatened U.S. tariffs targeting buyers of Russian oil, according to Reuters.