UPDATE 1-Pirates seize four ships in Gulf of Aden

(Recasts with Chinese ship, UN, Puntland comment)

By David Clarke

NAIROBI, Dec 17 (Reuters) - Somali pirates seized four ships in the Gulf of Aden on the same day the United Nations Security Council authorised countries to pursue the gunmen on land.

A Kenyan maritime group said pirates hijacked an Indonesian tugboat, a Turkish cargo ship, a Chinese fishing vessel and a yacht on Tuesday, all in one the world's busiest shipping lanes.

Rampant piracy off the coast of Somalia this year has earned gunmen millions of dollars in ransom, hiked shipping insurance costs and sent foreign navies rushing to patrol shipping lanes off the Horn of Africa nation.

The seizures have prompted some of the world's biggest shipping firms to switch routes from the Suez Canal and send cargo vessels around southern Africa instead -- which could push up the cost of commodities and manufactured goods.

While warships from several nations are patrolling the seas off Somalia and escorting ships, analysts say the problem must be tackled on land as well for any lasting solution.

The resolution passed by the 15-nation Security Council on Tuesday said states "may undertake all necessary measures in Somali, including in its airspace" to stop the pirates.

Andrew Mwangura of the Kenyan-based East African Seafarers Assistance programme said on Wednesday that Chinese fishing vessel Zhenhua-4 with 30 Chinese crew and a yacht with two on board had been seized off Yemen a day earlier.