* Indexes: Dow off 0.21 pct, S&P 0.15 pct, Nasdaq up 0.04 pct
By Chuck Mikolajczak
NEW YORK, Sept 23 (Reuters) - U.S. stocks inched lower open on Tuesday, as conflict in the Middle East intensified and the U.S. Treasury's move to curb "tax inversion" deals pulled healthcare stocks lower.
The United States and Arab allies bombed Syria for the first time on Tuesday, killing scores of Islamic State fighters and members of a separate al Qaeda-linked group, opening a new front against militants by joining Syria's three-year-old civil war.
The S&P healthcare sector lost 0.2 percent, weighed down by a 1.7 percent fall in AbbVie to $57.73. The Obama administration took several actions late Monday that will reduce the tax benefits available to companies that have done inversion deals, while also making new inversions more difficult and potentially less rewarding.
AbbVie has agreed to a deal to acquire Shire, which fell 1.9 percent to $251.38 in New York. Medtronic, which is working to close an inversion deal into Ireland with rival Covidien lost 3.3 percent to $63.78.
"Those are the stocks that are weak today, any of those companies that are in the process of using an inversion tax tactic," said Tim Ghriskey, chief investment officer of Solaris Group in Bedford Hills, New York.
"Most of those are healthcare names, perhaps they can justify them, but that is where we are certainly seeing some weakness day."
The Dow Jones industrial average was falling 36.36 points, or 0.21 percent, to 17,136.32, the S&P 500 was losing 3.01 points, or 0.15 percent, to 1,991.28 and the Nasdaq Composite was adding 1.70 points, or 0.04 percent, to 4,529.38.
Financial data firm Markit said its preliminary or "flash" September U.S. Manufacturing Purchasing Managers Index was unchanged from August's reading of 57.9, the highest since April 2010, and a touch below the 58 estimate.
The largest percentage gainer on the New York Stock Exchange was NQ Mobile, rising 15.6 percent, while the largest percentage decliner was Carmax, down 9.45 percent after reporting disappointing quarterly results.
Among the most active stocks on the NYSE were Grupo Aval Acciones, up 1.48 percent to $13.70; Bank Of America , up 0.82 percent to $17.17; and Rite Aid, up 3.82 percent to $5.31.
On the Nasdaq, Yahoo, up 1.1 percent to $39.08; Sirius XM, up 0.9 percent to $3.55; and APPLE, up 1.2 percent to $102.26 were among the most actively traded.
Declining issues were outnumbering advancing ones on the NYSE by 1,733 to 1,189, for a 1.46-to-1 ratio on the downside; on the Nasdaq, 1,383 issues were falling and 1,179 advancing for a 1.17-to-1 ratio favoring decliners.
The benchmark S&P 500 index was posting 2 new 52-week highs and 7 new lows; the Nasdaq Composite was recording 18 new highs and 98 new lows. (Reporting by Chuck Mikolajczak; Editing by Nick Zieminski)