MOSCOW: The Russian rouble fell against the dollar on Tuesday after investors worried about global trade tensions and the risk of new U.S. sanctions against Moscow bought dollars.

The dollar index was close to its highest level in more than a week against its rivals as investors feared emerging markets' export-oriented economies would be caught in the middle of any escalating trade conflict.

At 0855 GMT, the rouble was 0.1 percent weaker against the dollar at 68.18 and had gained 0.4 percent to trade at 78.83 versus the euro as the European currency fell against the dollar.

"There will be weakness in the national currency until there is clarity about potential U.S. sanctions (against Russia). That uncertainty could persist for one and a half to three months," analysts at BCS brokerage said in a note.

New U.S. sanctions, tied to an attack on a former Russian double agent in Britain, could be imposed on Russia in the autumn.

The market is also waiting for a decision from the U.S. Congress in the autumn about draft legislation that includes restrictions on investment in new Russian sovereign debt and bans several state-run Russian banks from operating in the United States.

Higher oil prices are providing some support to the rouble.

Brent crude oil, a global benchmark for Russia's main export, was up 1.25 percent at $79.16 a barrel, its highest level since July 10.

Russian stock indexes were up.

The dollar-denominated RTS index was up 0.17 percent to 1.087.16 points. The rouble-based MOEX Russian index was 0.35 percent higher at 2,354.18 points.