(Adds comment, updates throughout)
* Euro gains vs dollar, sterling, but fails to hold above $1.45
* Investors relieved Greek debt problems under control for now
* More euro gains possible on ECB rate rise speculation
By Naomi Tajitsu
LONDON, June 30 - The euro rose to a three-week high against the dollar on Thursday, swept higher by month-end demand which helped it extend a rally after Greece moved a step closer to securing international aid.
The single currency was also buoyed after comments from European Central Bank President Jean-Claude Trichet reinforced speculation that the ECB will raise interest rates next week, helping it to a 15-month high versus sterling.
Markets cheered the Greek parliament's passage of tough austerity measures on Wednesday, enabling the debt-stricken country to secure more emergency funding from the EU and the International Monetary Fund and staving off the threat of a debt default for now.
The euro hit a high of $1.4522 versus the dollar on trading platform EBS and analysts said further gains could propel it towards $1.5000. However, many remained wary about whether Greece will be able to implement such harsh measures and expected the euro's rise to be limited.
It failed to sustain a move above $1.4500, with traders saying demand from a semi-official European name and model funds ran into offers from sovereign names ahead of a reported options barrier at $1.4550.
"Euro zone rates are more likely to rise than those in the U.S. and the UK and this will keep the euro supported against the dollar and sterling," said Richard Wiltshire, chief FX broker at ETX Capital.
"But I can't see a huge reason to buy the euro as Greece is not out of the woods yet".
Athens on Thursday is expected to pass another vote on how to implement the plan, clearing the last obstacle to the release of 12 billion euros ($17.3 billion) of funding, which is essential to meet debt payments by mid-July.
It was last up 0.2 percent at $1.4460 against the dollar, with bids in the mid-$1.44 region seen as acting as support.
ETX's Wiltshire said the euro's gains were helped by hefty month-end buying of euro/sterling, some of which could reverse on Friday or next week.
The single currency was up 0.5 percent against the pound at 90.30 pence, having hit a 15-month high of 90.70 pence.
ECB RATE OUTLOOK
Bolstering the euro was the view that the European Central Bank will raise interest rates by 25 basis points to 1.5 percent next week, which would increase the single currency's rate advantage over the dollar.
Some analysts also saw further scope for short-term gains as talks progress on a second aid package for Greece, with investors taking the view that the euro zone debt crisis is under control for the time being.
"In the short term, at least, a Greece default is unlikely, and this is positive for the euro and also other risky assets," said You-Na Park, currency strategist at Commerzbank in Frankfurt, adding the euro could test $1.50 in the near term.
Others said more encouraging data in the U.S., including recent housing figures, and signs the Japanese economy may be recovering more quickly from its earthquake than expected, were helping to improve the broad outlook for the global economy through the second half of 2011.
Deutsche currency strategist Henrik Gullberg said this view would further stoke risk appetite, prompting investors to take on more long euro positions -- or bets to buy the currency -- after cutting back on those positions recently.
"Uncertainty about the global outlook, as well as Greece, has meant that a lot of long positions in risky currencies have been scaled back," he said.
At the same time, increasing concerns about the U.S. debt situation may sour sentiment for the dollar as Washington struggles to raise its budget limit.
Gains in the euro and other currencies considered higher risk, including the Australian and New Zealand dollars -- the latter hitting a post-float high in earlier trade -- knocked the dollar lower versus a currency basket.
The dollar index traded 0.25 percent lower as 74.503, having hit 74.255, its weakest since mid-June. It slipped 0.4 percent on the day to 80.40 yen . (Additional reporting by Jessica Mortimer; Editing by Anna Willard)