Updated

A Democrat and Republican on the Senate Foreign Relations Committee agreed Sunday that Russian President Vladimir Putin has ignored U.S. and European pleas to withdraw military troops from Ukraine and called for tougher economic sanctions, following a deadly shootout this weekend.

"I don't think Putin really believes we're going to punish them in that way," Tennessee GOP Sen. Bob Corker, the committee's senior Republican member, said on NBC's "Meet the Press."

Sen. Chris Murphy, a Connecticut Democrat and fellow committee member, said: "I think the time is now to rapidly ratchet up our sanctions, whether it's on Russian petrochemical companies or on Russian banks."

The senators made their comments after at least three people were killed in the Easter morning shooting and as tens of thousands of Russian troops occupy the Ukraine-Russian border and Moscow operatives purportedly infiltrate eastern Ukraine to stir opposition toward that country’s new, temporary government.

Both sides blamed each other for the shootout, at a checkpoint manned by pro-Russia insurgents in eastern Ukraine.

Russia's Foreign Ministry issued a statement blaming militant Ukrainian nationalists, and Russian state television stations aired pictures of supposed proof of their involvement in the attack.

The Ukrainian Security Service said the attack was staged by provocateurs from outside the country.

The clash, near the city of Slovyansk, appears to be the first since an international agreement was reached last week in Geneva to ease tensions in eastern Ukraine, where armed pro-Russia activists have seized government buildings in at least 10 cities. Russia last month annexed Ukraine’s Crimean Peninsula.

The political upheaval in Ukraine has been going on for months, with citizens in February ousting their Moscow-backed president.

The Russian ambassador to Ukraine told “Fox News Sunday” that his country is not on a military march into Eastern Europe and surrounding regions and blamed militia groups for the recent violence in Ukraine.

“We are not going anywhere,” Ambassador Sergey Kislyak said.

Kislyak repeatedly told Fox News that peace in that region cannot be achieved until “all” militia groups drop their weapons. And he attempted to downplay President Obama’s vow last week that additional economic sanctions will be imposed if Putin forces continue to fuel the unrest in Eastern Europe.

“We can withstand the pressures,” said Kislyak, suggesting the United States had returned to a Cold War mentality that has no place in the 21st century.

Obama has said his administration is prepared to take further action against Russia if diplomatic efforts to destabilize the conflict fail.

Vice President Biden plans to be in Kiev, the Ukrainian capital, on Monday and Tuesday to meet with government leaders and democracy advocates.

Corker, who plans to be in the region in May, also said the U.S. should be sanctioning some of the companies in the energy sector and large banks if Putin fails to immediately begin moving the 40,000 troops on the border, which are intimidating people in Ukraine.”

Geoffrey Pyatt, the U.S. ambassador to Ukraine, told CNN's "State of the Union” the international agreement forged late last week may be "the best chance that we have got to achieve a diplomatic de-escalation of this crisis."

However, he also said he’s seen reports of progress, including one Sunday morning that state at least one of the occupied government buildings now has a Ukrainian flag flying overhead.

The Associated Press contributed to this report.