* Maduro accuses U.S. and Colombia of assassination plot
* Guaido hit with travel ban, bank freeze
* Opposition plans more street protests
* Trump warns Americans to shun Venezuela (Adds Russia, Trump, PDVSA)
CARACAS/MOSCOW, Jan 30 (Reuters) - Venezuela's socialist leader Nicolas Maduro accused U.S. President Donald Trump of ordering his assassination while his main global backer Russia called on Wednesday for mediation in a standoff deepening geopolitical splits.
The fight to control Venezuela, which has the world's largest oil reserves, has intensified with new U.S. sanctions and legal moves that may bring the arrest of opposition leader and self-declared interim president Juan Guaido.
In an interview with Moscow's RIA news agency, Maduro, 56, facing the biggest challenge to his rule since replacing Hugo Chavez six years ago, said Trump had ordered neighboring Colombia to murder him.
"Donald Trump has without doubt given an order to kill me and has told the government of Colombia and the Colombian mafia to kill me," Maduro said, reprising a constant accusation of his and Chavez's over the years.
Bogota and Washington have routinely denied that, while foes say Maduro uses such accusations as a smokescreen when in trouble.
However, speculation of military action against him was fueled this week when Trump adviser John Bolton carried a notepad with the words "5,000 troops to Colombia".
In an early morning tweet, Trump warned U.S. citizens against traveling to Venezuela, given the unrest.
Russia, which like China has loaned and invested billions of dollars in OPEC member Venezuela, called on Guaido to drop his demand for a snap election and instead accept mediation.
However, given the failure of previous rounds of dialogue, including one led by the Vatican, opponents are suspicious, believing Maduro uses them to quell protests and buy time.
Venezuela's Supreme Court has imposed a travel ban on Guaido and frozen his bank accounts in apparent retaliation for oil sanctions imposed by the United States that are expected to severely hit an already collapsing economy.
The United States is Venezuela's largest crude importer, ahead of India and China, but the new measures limit transactions between U.S. companies and state oil company PDVSA.
Oil prices held steady on Wednesday, as Venezuela supply concerns were offset by the bleak global economic outlook. PDVSA bonds could be excluded from key indexes, also impacting sovereign paper, Bank of America Merill Lynch (BAML) said.
Guaido, the eldest of six children from a working-class family who emerged from virtual anonymity as a political activist, is recognized as president by the United States and most Western Hemisphere nations.
The 35-year-old opposition lawmaker, who is president of the National Assembly, says Maduro fraudulently won a second term last year and is offering an amnesty to military officials.
Maduro, who accuses Guaido of staging a U.S.-directed coup against him, still has the support of the top military brass, and is unlikely to back down unless that changes.
In the RIA interview, Maduro reiterated he was ready for talks with the opposition, but rejected calls for a snap election as blackmail.
"I won legitimately," he said. "If the imperialists want a new election, let them wait until 2025."
With the crisis deepening a showdown between Washington and Moscow across various global flashpoints, Maduro also expressed "pleasure and gratitude" for Putin's help.
Sources have told Reuters private military contractors who do secret missions for Moscow were in Venezuela.
A former union leader, bus driver and foreign minister, Maduro has overseen a shrinking economy and the migration of 3 million Venezuelans fleeing shortages and hyperinflation.
Guaido called for concentrations on Wednesday and a mass march at the weekend. More than 40 people have died so far in and around the protests that began a week ago, the U.N. human rights office said. Hundreds have also been arrested, including children.
"DEFEND THE FATHERLAND"
Government supporters have also attended large rallies led by Maduro allies, while the president visited military bases including overseeing live-fire exercises in recent days.
He ordered the creation of 50,000 popular defense units, community groups charged with the "integral defense of the fatherland."
Trump's top advisers include Cold War-era hawks and the Pentagon has refused to rule out military action, although most experts doubt that would happen.
U.S. Vice President Mike Pence met Guaido's designated envoy to the United States on Tuesday. Pence said they discussed recent sanctions actions, "highlighting that these deprive Maduro and his cronies access to corrupt income and ... preserve the country's wealth for the people of Venezuela."
The sanctions are likely to hit daily life hard in Venezuela, where public spending is almost entirely funded by oil. The government is eager to blame Guaido for the measures, which, once they begin to bite, could diminish his popularity.
Venezuelan Attorney General Tarek Saab sought a preliminary investigation of Guaido on the basis that he helped foreign countries interfere.
Announcing the investigation, the travel ban and the financial restrictions, Supreme Court President Maikel Moreno, a major Maduro ally, said the measures were to "protect the integrity of the country."
In a tweet, Bolton warned of "serious consequences for those who attempt to subvert democracy and harm Guaido."
(Reporting by Vivian Sequera; Additional reporting by Gabrielle Tétrault-Farber and Maria Kiselyova in Moscow; Susan Heavey in Washington; Karin Strohecker and Noah Browning in London; Writing by Frank Jack Daniel and Andrew Cawthorne; Editing by Peter Cooney, Alison Williams and Andrew Heavens)