A convoy of Ethiopian troops entered Somalia on Sunday, residents said, in a possible attempt to open a third front against al-Qaida-linked Somali insurgents.

The incursion into the central town of Guriel appears to be the largest movement of Ethiopian troops into Somalia since an unpopular Ethiopian invasion nearly five years ago.

The al-Shabab insurgents are already fighting an African Union force in the Somali capital and Kenyan troops in the south, where al-Shabab said it attacked a Kenyan warship on Sunday. The arrival of the Ethiopians would stretch al-Shabab further but could also hand it a propaganda victory if the insurgents are able to capitalize on the memories of Ethiopia's previous unpopular invasion.

The Ethiopians met with members of Somalia's Ahlu Sunnah Wal Jama militia in Guriel on Sunday afternoon, then moved into an army base in the south of the city, said Sheik Abdulle Abdi. He belongs to the militia, which is allied to the weak U.N.-backed Somali government and widely considered to be backed by Ethiopia.

Ahlu Sunnah Wal Jama supports traditional Sufi Islam and opposes the amputations and stonings carried out by al-Shabab.

However, Ethiopia's foreign ministry spokesman Dina Mufti denied that troops have crossed the border into Somalia. "That is not true," he said of the claims by residents.

But Guriel resident Ali Husein said he saw 21 vehicles carrying uniformed Ethiopian troops. "They waved at people then went to the south part of the town," he said.

Resident Shamso Hamsi also said he saw men wearing the uniforms of Ethiopian troops.

Ethiopia previously sent troops into Somalia in 2006 to defeat the Islamic Courts Union, the forerunner of al-Shabab. But residents complained that the Ethiopians mortared residential neighborhoods and shot indiscriminately when they were attacked. The killings of civilians helped galvanize nationalist sentiment that the Islamists used to recruit new fighters.

The Ethiopian force eventually left in 2009 as part of a peace deal, but the Ethiopian government has remained concerned about al-Shabab's activities and its ability to cross the country's long and porous border with Somalia. Neighboring Kenya is also concerned that Somalia's 20-year-old civil war is bleeding across its borders. Kenyan officials say that's why they sent troops into Somalia last month.

So far, fights between al-Shabab and Kenya have mostly been limited to skirmishes, but the militia claimed it destroyed a Kenyan warship early on Sunday as residents reported a gunbattle at sea lasting several hours.

Al-Shabab said it destroyed the vessel near Madhawa Island, just off the coast of Somalia near the Kenyan border, in a statement posted on a website the insurgents often use.

The militants' claims could not be immediately verified, and Kenyan defense spokesman Maj. Emmanuel Chirchir said that no Kenyan ships had been destroyed.

Residents in Somalia's coastal Kudha town said they heard gunfire and explosions at sea.

The gunfight early Sunday morning lasted more than two hours and then at dawn residents saw three speedboats heading toward the insurgent-held port city of Kismayo, said Ali Abdulahi.

Maj. Chirchir said in a statement Sundaythat Kenyan jets supported by naval gunfire had destroyed two al-Shabab training camps near the coast. It was unclear if he was referring to the same incident.

Somalia has not had a functioning central government for more than 20 years. The current incursions mark the highest rate of international intervention in the failed state for a generation.

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Associated Press writer Luc Van Kemenade contributed to this report from Addis Ababa, Ethiopia.