International maritime officials say the MV Al Khaliq was seized Thursday about 330 kilometers west of the Seychelles islands.
Officials say the ship is carrying 26 crew members -- 24 Indians and two Burmese.
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The European Union's anti-piracy mission says crew members radioed for help before losing contact. An EU aircraft that flew over the scene reported seeing six pirates on board and the Al Khaliq towing two pirate skiffs.
The EU and NATO say pirates fired on another ship, the Italian-flagged MV Jolly Rosso, off the coast of Kenya Thursday. They say that ship managed to escape.
The Al Khaliq is the fourth ship Somali pirates have hijacked this month, and the third in the past week.
Chinese officials have said they are considering a military operation to rescue a Chinese bulk carrier hijacked Monday with 25 people on board. Pirates have said they will kill the crew members if any rescue is attempted.
Somali pirates have hijacked dozens of ships over the last two years, taking in tens of millions of dollars in ransom money. The pirates are believed to be holding seven ships in all.
A new report on the pirates says current international strategies to stop the hijackings will not work.
The report, put out by the Norwegian Institute for Urban and Regional Research, says the international naval patrols off Somalia's coast are expensive, and that the pirates can evade the patrols or escape to shore.
It says efforts to combat piracy by strengthening Somalia's Western-backed government are limited, because the pirates come from specific regions and clans, far away from the capital.
But the researchers say there are centers of power, close to the pirate bases, and that these can be allies in fighting piracy. The researchers say that to effectively combat piracy, the international community needs to support these local structures.
Some information for this report was provided by AFP, AP.