A top Republican senator is urging President Donald Trump to provide Ukraine with lethal defensive aid as the fight there against Russian-backed rebels has again intensified in recent days.

“In the first of what will be many tests for your new administration, Russia and its proxy forces launched attacks against Ukrainian forces this week, killing at least seven Ukrainian soldiers and wounding dozens more," Arizona senator John McCain wrote in a Wednesday letter. "Vladimir Putin's violent campaign to destabilize and dismember the sovereign nation of Ukraine will not stop unless and until he meets a strong and determined response."

"I urge you to exercise the authority given to you by the National Defense Authorization Act for Fiscal Year 2017 to provide defensive lethal assistance to Ukraine to defend its territory against further violations by Russia and its separatist proxies."

McCain also urged the president to maintain existing sanctions on Russia, including those levied after the annexation of Crimea in 2014. He advised ramping up sanctions based on the country's interference in elections.

Secretary of State Rex Tillerson, who was confirmed Wednesday, backed lethal defensive aid to Ukraine during his confirmation hearing. Other portions of the Trump team have reportedly been less supportive, working to scale back language in the GOP platform on providing such aid to Ukraine last summer.

Ahead of a sharp spike in fighting in eastern Ukraine Sunday, Trump discussed the ongoing conflict with Russian president Vladimir Putin and agreed to "build up partner cooperation" on that issue among others, according to a Kremlin readout. It remains to be seen how the president will balance congressional calls to arm Ukrainians fighting Russian-backed rebels with his stated desire to improve relations with the Kremlin.

Republican senators, including McCain, told THE WEEKLY STANDARD in November they were unsure where Trump would land on providing lethal aid to Ukraine, but said they would nonetheless continue pushing for it.

"I honestly don't know enough about what their position will be," McCain said. "I'll continue to push for providing defensive weapons to Ukraine. I'll continue that effort. But I can't guess on what the Trump administration [will do]."

South Carolina senator Lindsey Graham, Florida senator Marco Rubio, and Senate Foreign Relations Committee chairman Bob Corker also told TWS they were not sure where the Trump administration would be on the matter.

President Barack Obama opposed providing lethal defensive aid to the Ukrainians, opting instead for nonlethal assistance.