UPDATE 3-German-owned tanker hijacked in Gulf of Aden

(Adds Kenya-U.S. agreement)

By Wangui Kanina

NAIROBI, Jan 29 (Reuters) - Somali pirates hijacked a German-owned tanker carrying liquefied petroleum gas on Thursday, the first ship seized in the Gulf of Aden in nearly four weeks.

A decline in the rate of successful attacks since foreign navies rushed to the busy sea lane has raised optimism among shippers that the menace was being curbed, but pirates have been seeking ways to evade the warships.

The Longchamp was hijacked with a crew of 12 Filipinos and one Indonesian as it was headed from Europe to the Far East, Andrew Mwangura, of the East African Seafarers Assistance Programme, told Reuters.

Hamburg-based ship operator Bernard Schulte Shipmanagement confirmed the hijacking. It said no demands had been made.

"The master was briefly allowed to communicate with us and it appears that all crew members are safe," it said in a statement on its website.

Shipping information service Lloyd's List put the Longchamp's size at 4,316 deadweight tonnes -- over 70 times smaller than the Saudi supertanker held in November and released on Jan. 9 after the world's biggest ship hijacking.

Liquefied petroleum gas, a fuel, is highly flammable.