* Investors watching situations in Greece, Ukraine
* S&P 500 hits intraday record high
* Celsus shares plummet after drug fails study
* Indexes: Dow up 0.1 pct; S&P 500 up 0.1 pct; Nasdaq up 0.02 pct (Updates to late trading)
By Caroline Valetkevitch
NEW YORK, Feb 17 (Reuters) - U.S. stocks inched higher on Tuesday, pushing the S&P 500 above 2,100 to another record intraday high as optimism grew that a debt deal would be reached with Greece.
A source told Reuters that Greece intends to ask for an extension of a loan agreement tomorrow. The report follows a collapse of deal negotiations on Monday, which led to European Union finance ministers pressuring the country to remain in an international financial rescue program.
U.S.-listed shares of the National Bank of Greece were up 1.6 percent after falling more than 13 percent earlier in the session.
The news was viewed as another sign of progress, building on the recent optimism that contributed to major indexes notching a second straight week of solid gains last week.
Despite that, investors continued to monitor the situation cautiously, while a fragile Ukraine truce added to the market's uncertainty.
Among the day's biggest positives, shares of Medical device maker Medtronic Plc, which last month completed the $49.9 billion purchase of Ireland-based Covidien Plc, were up 3.6 percent at $78 after it reported a better-than-expected third-quarter profit, driven by solid growth in its cardiac and vascular business.
The Dow Jones industrial average rose 15.55 points, or 0.09 percent, to 18,034.9, the S&P 500 gained 1.94 points, or 0.09 percent, to 2,098.93 and the Nasdaq Composite added 0.74 points, or 0.02 percent, to 4,894.57.
In eastern Ukraine, Pro-Russian rebels fought their way into an encircled government bastion and were battling street-to-street, all but dashing hopes that a European-brokered peace deal would end months of conflict.
While the United States has little direct exposure to Greece, Ukraine or Russia, any breakdown in either place could lead to continued volatility in Europe, a major trading partner.
Shares of Transocean Ltd fell 0.5 percent to $18.96 a day after the company slashed its dividend and said its chief executive stepped down.
Also on the downside, Celsus Therapeutics plummeted 81 percent to $1.20 after the company's lead drug failed a mid-stage study. VBL Therapeutics Inc dropped 64.6 percent to $5 after it said it would stop developing its experimental inflammatory drug to fight ulcerative colitis and psoriasis.
Declining issues outnumbered advancing ones on the NYSE 1,713 to 1,354, for a 1.27-to-1 ratio; on the Nasdaq, 1,495 issues rose and 1,211 fell for a 1.23-to-1 ratio favoring advancers.
The benchmark S&P 500 index was posting 61 new 52-week highs and 2 new lows; the Nasdaq Composite was recording 108 new highs and 18 new lows. (Editing by Nick Zieminski)