KYIV, March 6 (AFP) - Ukrainian President Volodymyr Zelenskyy announced that he spoke by phone with his US counterpart Joe Biden on Sunday to discuss financial support and sanctions against Russia as his country faces an intensifying onslaught.

"As part of the constant dialogue, I had another conversation with @POTUS," Zelenskyy tweeted. "The agenda included the issues of security, financial support for Ukraine and the continuation of sanctions against Russia."

Biden welcomed the decisions by Visa and Mastercard to suspend their operations in Russia, the White House said on Saturday.

"President Biden noted his administration is surging security, humanitarian, and economic assistance to Ukraine and is working closely with Congress to secure additional funding," a White House readout of the call added.

Hours earlier, the Ukrainian leader had addressed US lawmakers by video call, pleading for further assistance to his besieged country and a blacklisting of Russian oil imports.

The American legislators promised an additional US$10 billion aid package, but the White House has so far ruled out an oil ban, fearing it would ratchet up prices and hurt US consumers already stung by record inflation.

Weapons, ammunition and funds have poured into Ukraine from Western allies, which have also imposed sweeping sanctions as they seek to bolster Kyiv against Moscow's invasion, which began Feb 24.

Washington last week authorised US$350 million of military equipment -- the largest such package in US history.

While visiting Ukrainian refugees on the Polish border over the weekend, US Secretary of State Antony said that Washington was seeking US$2.75 billion to help address the humanitarian crisis unfurling as nearly 1.4 million civilians flee.