Nine Somali pirates were still holding a Yemeni oil tanker in the Gulf of Aden and a rescue operation by Yemeni naval and coast guard forces was ongoing, the Defence Ministry said, retracting an earlier statement that said the ship was freed, according to dpa. "Nine pirates are still on board the ship and the operation is ongoing to recover it," the ministry said in a statement posted on its web site. "Forces are preparing to storm the ship backed by military helicopters," the statement said. The ministry said in a previous statement that the Yemeni navy forces were in control of hijacked ship. It did not clarify the reason behind the contradiction in statements. Coast guard sources earlier told the German Press Agency dpa that two pirates were killed and three pirates and two Yemeni soldiers were injured in the clashes. They said four more pirates were arrested in the operation. The sources said two navy ships were sent to aid coast guards gunboats involved in a gunfight with the pirates. A government official said the tanker was not carrying cargo when the pirates attacked it off the Yemeni coast earlier in the day. Twenty-three seafarers, including three Indians, were on board the vessel, he added. The official said the vessel was sailing from the Arabian Sea Yemeni port of Nashtoon to the southern port city of Aden when the pirates hijacked it about 10 miles off the south-eastern port of Balhaf. According to coast guard sources, the bandits had tried to seize three other vessels sailing along with Qana, but they failed to board them. Separately, Somali pirates on Sunday freed the Yemeni tanker carrying more than 2,000 tons of diesel they seized on January 3, Yemeni officials said. Fifteen crew members were also released, the officials said. The release of the vessel, Sea Princess II, was secured through negotiations, the officials said, refusing to say whether a ransom was paid. The tanker was en route from the Gulf of Aden to Nashtoon when the pirates attacked it and diverted it to the Somali coast. The issue of piracy in the waters off Somalia, which is generally recognized as a failed state, have created an international crisis for shipping, with the US Navy and warships from European Union countries now attempting to patrol the seas off the Horn of Africa.