A top Obama adviser said Wednesday that the administration is considering lethal arms for Ukraine and said he believed it could deter Russia from further aggression against the Eastern European nation.

Deputy national security adviser Tony Blinken acknowleged though that the administration has been reluctant to act, fearing that Russia could step up its support for armed separatists.

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"Part of the reason has been that in our judgment, as much as we're able to throw at the Ukrainians in terms of lethal support, unfortunately if the Russians choose to, they will outmatch that easily," Blinken told the Senate Foreign Relations Committee at a hearing on his nomination for the No. 2 post at the State Department.

"That said, what we've seen in recent days and in recent weeks, including the blatant violation by Russia of the very agreement it's signed, the Minsk accords, [defensive lethal assistance] remains on the table. It's something that we're looking at," he added.

Republican lawmakers are urging the president to consider providing Ukraine with lethal arms, over fears of a new build-up of Russian military forces along its border.

Russia annexed the Ukrainian peninsula of Crimea in March, and has been supporting pro-Russian separatists in Eastern Ukraine with military assistance.

Although the U.S. has provided about $100 million in non-lethal military assistance, President Obama has so far been unwilling to provide Ukraine with weapons it has requested, over concerns it would further provoke Russia.

Blinken said he was sure the issue would be discussed during Vice President Joe Biden Joe BidenBiden leads Trump by 36 points nationally among Latinos: poll GOP set to release controversial Biden report Can Donald Trump maintain new momentum until this November? MORE's trip to Ukraine this week.

Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) hammered Blinken for not giving a "yes or no" answer when asked if he would recommend arming Ukraine to Secretary of State John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE if confirmed.

"That is a straightforward question...You're supposed to be coming before this committee and give us your views," said McCain, who supports providing lethal arms.

"My belief is that that can play a role potentially in deterring [Russia]," Blinken said. "I believe that is something we need to look at very actively."

"So let the record show, Mr. Chairman, that the witness would not answer the question," McCain said. "After 4,000 dead, and a country dismembered, and 4,000 more Russian troops invading Eastern Ukraine, and you think it's something to be looked at?"

Blinken said the U.S. has provided Ukraine with more than $100 million in non-lethal military aid, including meals-ready-to-eat, blankets, night vision goggles, protective vests, counter-mortar radar, and communications and transportation gear.

Blinken said sanctions imposed by the U.S. and the European Union were having a "significant impact on the Russian economy," but agreed that Russian President Vladimir Putin had not been deterred.

The hearing with Blinken gave lawmakers an opportunity to grill a White House official on other national security matters, including U.S. efforts against the Islamic State in Iraq and Syria and a potential nuclear deal with Iran.

Blinken said he agreed Congress should pass a "targeted, focused" authorization for use of military force (AUMF) against ISIS and that the White House would "welcome" such legislation.

He also said a proposal by Sen. Bob Menendez Robert (Bob) MenendezKasie Hunt to host lead-in show for MSNBC's 'Morning Joe' Senators ask for removal of tariffs on EU food, wine, spirits: report VOA visa decision could hobble Venezuela coverage MORE (D-N.J.) that would limit authorization to three years or "some other reasonable timeframe," and foreclose the possibility of a "large-scale enduring ground combat mission" would "be appropriate."

"I think the elements you've laid out as a general matter would be appropriate," he told Menendez, chairman of the Senate panel. "Those [elements] would seem to me to form a good basis for a conversation on developing a new AUMF."

Blinken said the question is finding language that would win broad bipartisan support, and added that he has engaged with Sen. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R-Tenn.), ranking member of the committee.

"You have not engaged with me, that is totally untrue," Corker snapped.

"Going forward from today, we will actively engage on an AUMF," Blinken responded. "The short answer is, we want to work with you on that in the days and weeks ahead."

Blinken also addressed the nuclear talks with Iran which face a Monday deadline.

"Right now I think it's going to be difficult to get where we want to go," he said, adding that a deal by Nov. 24 was "difficult but not impossible."

He sought to assure lawmakers that the U.S. would not accept a bad deal. He said the White House wanted to keep sanctions in place as long as possible. Any sanctions relief could be "snapped back with some automaticity" in the case of any violations, he said.

"We would not even suspend sanctions until Iran has taken signification actions," said Blinken.