NAIROBI, Kenya — Somali pirates attacked on oil tanker Monday farther out at sea than any previous assault, suggesting that pirate capabilities are growing as they increase activity off East Africa.

Pirates in two skiffs fired automatic weapons and rocket-propelled grenades at the Hong Kong-flagged BW Lion about 1,000 miles (1,600 kilometers) east of the Somali coast, the EU Naval Force said.

The tanker's captain increased speed and took evasive maneuvers, avoiding the attack, the force said. No casualties were reported. The naval force sent a plane from the island nation of Seychelles to investigate.

Pirates have launched increasingly bold attacks against vessels in the Indian Ocean and Gulf of Aden in hopes of capturing a ship and crew and collecting ransom. They currently hold more than 190 hostages, including a British couple seized from their personal yacht late last month.

The high-seas hijackings have increased despite an international armada of warships deployed by the United States, the European Union, NATO, Japan, South Korea and China to patrol the region. U.S. drones launched from nearby Seychelles are also patrolling the region for pirates.

Spain on Monday raised the possibility of sending two captured Somali pirates back home after trying them in Madrid — as a way to win the release of a Spanish trawler held by fellow brigands off the Horn of Africa.

Pirates seized the ship Alakrana and its 36-member crew in the Indian Ocean Oct. 2, and besides a ransom they are demanding the release of two colleagues who were caught the next day by Spanish naval forces. Among the 36 hostages are 16 Spaniards, eight Indonesians, and 12 crew from five African countries.

Justice Minister Francisco Caamano told reporters that Spain would have to try the two in Madrid on kidnapping and other charges "and then see if there is some kind of international agreement" allowing them to serve their sentence in Somalia.

Judge Baltasar Garzon, who ordered the two pirates brought to Madrid, said: "I think there are legal avenues to resolve this conflict. I sincerely think it can be done."

Garzon declined to go into detail. Such a decision would not be up to him, but rather his superiors at the National Court. He insisted, however, that Spain cannot yield to the hijackers and simply free the two men held in Madrid.

Prime Minister Jose Luis Rodriguez Zapatero, speaking during a visit to Poland, declined to confirm or deny that Spain is considering trying the two and then sending them home to serve their sentence.