GAZA, Aug 20 (Reuters) - Palestinian militant group Hamas said it fired two rockets at an Israeli gas installation about 30 km (19 miles) off the coast of Gaza on Wednesday in the first apparent attack of its kind.

The Israeli military said no missiles had struck any gas platforms at sea.

The armed wing of Hamas, engaged in a six-week war with Israel, said on its website it had fired two rockets at Noa, a gas well owned by Nobel Energy and Delek.

Noa lies northwest of the Gaza Strip in Yam Tethys, a largely depleted gas field. "The gas is flowing, business as usual," a spokeswoman for Nobel said in an emailed statement. Delek had no immediate comment.

While Noa is technically within range of Hamas rockets, the weapons are highly inaccurate and the chances of hitting a relatively small platform at sea are extremely unlikely.

At the same time, Israel's offshore gas reserves have attracted large foreign investment and the country is keen to ensure security, with the navy believed to provide heavy protection. Defence officials are reluctant to provide details.

Earlier in the conflict, shrapnel from a Hamas rocket landed near Ben Gurion airport east of Tel Aviv, Israel's international hub, prompting U.S. and European airlines temporarily to suspend flights -- a blow to Israel's economy and reputation.

A ceasefire between Israel and the Hamas militants who control Gaza collapsed on Tuesday, ushering in a new round of rocket launches and Israeli airstrikes, with no sign of any lasting peace deal in sight.

(Reporting by Nidal al-Mughrabi and Noah Browning and Steven Scheer; Writing by Maayan Lubell; Editing by Crispian Balmer)