Tokyo stocks opened flat on Monday after three days of gains, as cautious investors watched developments in the FBI probe into alleged Russian meddling in the US election.

The benchmark Nikkei 225 index was up 0.01 percent, or 2.94 points, at 22,821.97 in early trade while the broader Topix index gained 0.16 percent, or 2.92 points, to 1,799.45.

It will be "a week of patience" as investors keep a wary eye on US political developments and economic indicators, Okasan Online Securities said in a note.

But a weaker yen, which is positive for Japanese exporters, helped prop up the market.

"'The Russia-gate', unless it stalls US tax reform, would only have a limited impact on (Tokyo) markets," Okasan added.

Among economic data to be released this week is a key US jobs report due out on Friday.

In an ominous turn for President Donald Trump, his former security advisor Michael Flynn on Friday pleaded guilty to lying to the FBI and pledged to cooperate with a special prosecutor.

The Russia meddling probe darkened what would otherwise have been a triumphant week for Trump as his key tax reform bill nears passage.

The dollar rose to 112.75 yen early Monday from 112.12 yen in New York Friday afternoon on the Senate's passage of the most significant US tax overhaul in 31 years.

In stocks trade, oil explorers were up, with Inpex rising 1.50 percent to 1,319.5 yen.

Major banks were also up. Mitsubishi UFJ rose 0.78 percent to 804.5 yen and Mizuho Financial gained 0.34 percent to 204.45 yen