* Investors jittery after proposal to tax Cypriot deposits * Focus on Cyprus parliament vote, peripheral bond yields * Euro/dollar technical indicators show sell signal By Gertrude Chavez-Dreyfuss NEW YORK, March 18 (Reuters) - The euro tumbled to a more than three-month low against the U.S. dollar and a roughly two-week trough versus the yen on Monday as a bailout plan for Cyprus that will tax bank deposits spurred contagion worries in the euro zone. Euro zone finance ministers demanded at the weekend that Cypriots pay up to 9.9 percent of their bank deposits in exchange for a 10-billion-euro ($13 billion) bailout. The move broke with previous EU protocol that citizens' savings are sacrosanct and led to worried Cypriots emptying cash machines on the island. "There is a very real possibility of a run on the banks, people are lined up at the ATMs as we speak; I cannot believe that they (European officials) didn't see this coming," said Sean Cotton, vice president and foreign exchange advisor at Bank of the West in San Ramon, California. "The question is, could this happen to other countries? I am by no means an 'oracle', but right now, I am diligently searching for any and all companies that produce mason jars and or mattresses; I have a feeling they are going to make a killing." The speaker of Cyprus's parliament said lawmakers will vote on the plan Tuesday, postponing the vote by a day, as the government works on a plan to soften the blow for small savers. Analysts said any changes to help smaller depositors could limit euro losses but overall the euro would remain vulnerable. The euro dropped to a three-month low of $1.2880 in Asian trade, before paring losses to last trade down 0.9 percent on the day at $1.2960. Most investors are likely to use a bounce to initiate fresh bets against the euro. Scotiabank chief currency strategist Camilla Sutton said all the technical signals are in 'sell' territory in the euro/dollar pair, with the relative strength indicator not yet in oversold territory. Against the yen, the euro fell 1.2 percent, briefly breaking through support at 121.68 yen, its 55-day moving average. It dropped as low as 121.55, the lowest since March 6. It was last at 123.14 yen, down 1.1 percent. Yields on bonds of struggling euro zone countries such as Spain and Italy rose while those on safe-haven German bunds fell, with investors wary of any sign of contagion from Cyprus. Reflecting that nervousness, in the options market one-month euro/dollar implied volatilities jumped to 13.33 percent in New York trading from around 7.7 percent on Friday. Euro/dollar one-month risk reversals, which measure the relative demand for options on the euro rising or falling, were showing a growing preference for euro weakness. The euro fell 0.2 percent against the Swiss franc to 1.2248 francs and 0.8 percent against the British pound to 85.75 pence. Both the franc and the pound are bought when risks to the euro zone debt crisis escalate. YEN FIRM The yen was also higher. Many investors consider the highly liquid Japanese currency a safe haven and so it is sought during times of economic uncertainty and financial market stress. The dollar dropped to as low as 93.45 yen on trading platform EBS, where yen flows are the largest. On the Reuters platform, the dollar/yen low was 94.03. The pair has moved away from a 3-1/2-year peak of 96.71 yen struck on March 12. It was last down 0.3 percent at 94.90 yen. However, some strategists said the yen's strength would be short-lived given bets on more aggressive easing steps from the Bank of Japan, and expectations euro zone politicians will be able to reassure markets. Given the dollar's solid gains against the euro, the U.S. currency rose 0.2 percent against a basket of currencies to 82.454. An improving economy in the United States has underpinned the dollar in recent weeks. Data released on Friday showed U.S. manufacturing was growing, although consumer sentiment in the world's biggest economy faltered to its weakest in over a year and inflation picked up.