STOCKHOLM, April 28 (Reuters) - The Stockholm District Court extended the detention of two Swedish citizens suspected of financing terrorism in Somalia, a public prosecutor said on Monday.

Public prosecutor Ronnie Jacobsson said the court ordered the extention until May 8 of two men of Somali origin held on suspicion of collecting money and sending it to al Shabaab, a militant group that Sweden considers a terrorist organisation.

The two, aged 42 and 38, were taken into custody on February 28 after joint raids in Sweden and Norway led to the detention of six people.

"They both have told us they are politically active in Somalia," Jacobsson told Reuters. "They are accused of collecting money from the Swedish Somali network and sending money to them (Al-Shabaab)."

Washington has also branded al Shabaab as terrorists. The Islamist group has led an insurgency against the Somali government and its Ethiopian allies since early 2007.

The prosecutor said he was certain the case would not be ready by May 8 and that he would need to apply for a further extension. "We had hoped it could be finished at the end of May, but I'm beginning to doubt that," he said.