Ukraine's President Volodymyr Zelensky has called on the United States to strengthen sanctions on Russia, saying Moscow "violated" agreements made on halting strikes on energy infrastructure and on Black Sea.
"I believe we have come to the point of increasing the sanctions impact, because I believe that the Russians are violating what they have promised America.
"At least what America has told us, and publicly," President Zelensky said at a news conference in Kyiv.
"We very much hope that President (Donald) Trump has all these appropriate tools to increase the sanctions pressure on the Russian side."
Last week, the US said that it had made separate agreements with Ukraine and Russia to ensure safe navigation in the Black Sea and to implement a ban on strikes against energy facilities in the two countries.
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Meanwhile, Russia said that is in working with the US on ideas for a possible peace settlement in Ukraine and on building bilateral ties.
The statement came after President Trump said that he was angry with Vladimir Putin after the Russian leader criticised the credibility of Mr Zelensky.
In an interview with NBC News, Mr Trump also suggested that he could impose secondary tariffs of 25-50% on buyers of Russian oil.
He later reiterated to reporters that he was disappointed with Mr Putin but added: "I think we are making progress, step by step".
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Trump calls out both Putin, Zelensky over ceasefire talks
Asked about Mr Trump's comments, Russian government spokesman Dmitry Peskov said that Mr Putin remains open to contacts with Mr Trump and is continuing to work with the US.
"We are continuing to work with the American side, first of all to build our bilateral relations, which were badly damaged during the previous (US) administration," Mr Peskov said.
"We are also working on the implementation of some ideas related to the Ukrainian settlement. This work is under way, but so far there are no specifics that we could or should tell you about. This is a time-consuming process, probably due to its complexity," he added.
A call between Mr Trump and Mr Putin, he said, could be arranged at short notice if necessary, though none was scheduled for this week.
Mr Trump has that he wants to be remembered as a peacemaker and to end the three-year conflict in Ukraine.
He also warned of the risks of it escalating into a world war between the US and Russia.
He reiterated yesterday that he would impose secondary tariffs if Mr Putin did not cooperate.
"I want to see him make a deal so that we stop Russian soldiers and Ukrainian soldiers and other people from being killed," he told reporters in Washington.
"I want to make sure that he follows through, and I think he will."
Since taking office in January, President Trump has shifted the US to a more conciliatory stance towards Russia that has left Western allies wary as he tries to broker an end to the war.
His comments about Mr Putin reflect his growing frustration about the lack of movement on a ceasefire.
"If Russia and I are unable to make a deal on stopping the bloodshed in Ukraine, and if I think it was Russia's fault ... I am going to put secondary tariffs on oil, on all oil coming out of Russia," Mr Trump told NBC.
"That would be, that if you buy oil from Russia, you can't do business in the United States.
"There will be a 25% tariff on all oil, a 25- to 50-point tariff on all oil," he added.
China and India buy about 80% of Russian crude exports. Chinese traders said they were unfazed by the threat, while China said its cooperation with Russia was neither directed against, nor affected by, third parties. India declined to comment.
Minerals cooperation has been floated by both Ukraine and Russia, although President Trump said that Mr Zelensky wanted to back out of a proposed deal.
Russia and the US have started talks on joint rare earth metals and other projects in Russia, and companies have expressed an interest in them, President Putin's investment envoy, Kirill Dmitriev, said.
"There are no specifics here yet, but the interest is evident. The interest is mutual because we're talking about mutually beneficial projects," Mr Peskov said.
