A cross-border drone attack from Sudan killed 17 people in Chad including mourners attending a funeral service, the Chadian government and local sources said on Thursday, and the country's president vowed to retaliate for any further attacks.

The border town of Tine was struck on Wednesday afternoon as mourners gathered at a house for a funeral ceremony for a dead relative that involved reading the Koran, a local resident said.

There were two explosions and casualties included mourners and children who had been playing nearby, said the resident, who declined to be identified for security reasons.

Local government sources said it was not immediately clear who was behind the attack.

The conflict in Sudan between the Sudanese army and the paramilitary Rapid Support Forces (RSF), which began in April 2023, has periodically spilled into Chadian territory, causing casualties and property damage.

Sudan's army and the RSF issued statements blaming each other for the attack. Sudan's army offered "sincere condolences and deepest sympathies to the families of the victims" and to Chad's government and people.

Chad closed its eastern border with Sudan last month after clashes linked to the war killed five Chadian soldiers.

In a statement issued early on Thursday, the government said Chad had strengthened its security presence at the border and could potentially carry out operations on Sudanese territory.

The office of Chad President Mahamat Idriss Deby said in a statement late on Wednesday that Deby had ordered the army to retaliate against any attack from Sudan.

Two local government sources had earlier put the toll at 16 killed and 10 wounded. A military source said all the dead and injured were civilians.