* Nikkei gains early but makes about turn after US missile strikes
* Defence-related shares up, Ishikawa Seisaku rallies
By Shinichi Saoshiro
TOKYO, April 7 (Reuters) - Japan's Nikkei share average hit a four-month low on Friday after a U.S. missile strike on Syria hurt broader risk sentiment.
The Nikkei was down 0.1 percent at 18,577.92 after slipping to as low as 18,517.43, its weakest since Dec. 7.
The index had risen as much as 1 percent earlier in the session, getting a lift from an initially weaker yen and overnight gains by Wall Street shares.
But stocks made an about-turn as risk sentiment quickly soured on news that the United States had launched cruise missile strikes on an airbase in Syria, responding to a deadly poison gas attack that Washington has blamed on Syrian President Bashar al-Assad's forces.
"The market took a first knock as the yen jumped on risk aversion that stemmed from the news of the U.S. strikes. That led to a sell-off in the stock market initiated by falling futures," said Chihiro Ohta, equity general manager at SMBC Nikko Securities.
The dollar was down 0.5 percent at 110.250 yen, pulled down from a high of 111.000 struck before the U.S. launched its missile strikes.
Shares of companies related to defence swam against the tide. Ishikawa Seisaku, a manufacturer of land mines, rallied 15.2 percent and was the top gainer.
Howa Machinery, a machine maker that supplies rifles and mortars to Japan's self-defence force, added 1.3 percent and Tokyo Keiki, which makes navigation systems for military use, rose 1.2 percent.
Seven & i Holdings advanced 3.6 percent after the convenience store operator reported a 3.5 percent operating profit gain in the year through February 2017. News that Seven & i would buy more than a thousand convenience stores from Texas-based Sunoco LP to beef up its U.S. operations also provided a lift.
Yamato Holdings Co rose 3.2 percent after a report that the package deliverer will stop making same-day deliveries for Amazon, lending substance to hopes that Yamoto would trim unprofitable sectors of its business.
The broader Topix was up 0.2 percent at 1,483.44 and the JPX-Nikkei Index 400 climbed 0.25 percent to 13,291.20. (Reporting by Shinichi Saoshiro; Editing by Eric Meijer)