(Updates number of sponsors, add details of proposed legislation)
By Patricia Zengerle
WASHINGTON, April 30 (Reuters) - A group of Republican U.S. senators introduced legislation on Wednesday proposing their own measures to punish Russia over the Ukraine crisis, including sanctions on major banks and energy companies, as well as $100 million in military aid for Kiev.
Saying they were frustrated with President Barack Obama's reaction to Russia's military action in Ukraine, the lawmakers said the package would also require Obama to increase substantially U.S. and NATO support for the armed forces of Poland, Estonia, Lithuania and Latvia and accelerate implementation of missile defense in Europe.
The legislation provides authority for exports of U.S. natural gas to all World Trade Organization members, a demand of Republicans since the Ukraine crisis began, and provides support to encourage U.S. companies to invest in energy projects in Ukraine, Georgia and Moldova.
Backers of the bill included Senator Bob Corker of Tennessee, John McCain of Arizona and other leading Republican foreign policy voices. Corker, the top Republican on the Senate Foreign Relations Committee, called Obama's response to the crisis "tepid" and "cautious."
"We want put real sanctions in place that have an effect on the Russian economy," he told a news conference.
Sponsors said at the news conference the measure had 19 co-sponsors, but the number rose to 21 later in the day.
The bill also seeks immediate new sanctions on four Russian banks: Sberbank, VTB Bank, VEB Bank , Gazprombank, as well as energy firms Gazprom, Novatek and Rosneft, and Rosoboronexport, a major Russian arms exporter.
There was no immediate word on whether the Senate, which is controlled by Obama's fellow Democrats, would vote on the bill. Democratic aides said neither Democratic leaders nor the Senate Foreign Relations Committee had seen the measure.
Maryland Democratic Senator Ben Cardin, a senior member of the foreign relations panel, told Reuters he preferred Obama's more incremental approach to sanctions, including working closely with European allies and supporting the Ukraine economy.
"But I can understand, knowing the partisan nature here in Congress, that this would be an area that they (the Republicans) would use to underscore their displeasure with the Obama administration, which is unfortunate," he said.
(Reporting by Patricia Zengerle; Editing by Sandra Maler, Eric Beech and Meredith Mazzilli)