Chad's military has said it killed more than 200 Boko Haram fighters on Tuesday in a gun battle in north east Nigeria.

Chadian troops entered Nigeria from Cameroon earlier on Tuesday after a campaign of air strikes against the militant group.

In total, Chad has deployed 2,500 troops as part of a broader regional effort to subdue militants, who want to establish a state in Nigeria's north east.

Fighting around the towns of Gambaru and Ngala on Tuesday resulted in the deaths of 20 militants, as well as the destruction of more than a dozen vehicles equipped with heavy weapons, along with 100 motorcycles, the Chadian army said in a statement.

The claim was not verified by independent sources.

Attacks on the militants have assumed a regional dimension, with Nigeria working with its neighbours in a bid to defeat the group which has terrorised the region since it was established in 2009. Around 10,000 people died in the north east Nigeria in 2014.

Boko Haram fighters also attacked the town of Fotokol in Cameroon on Wednesday, although they were repelled after several hours of fighting.

"The insurgents have been driven out. They tried to surprise us because the Chadian troops who were in Fotokol had crossed over to Nigeria," said Cameroon's information minister Issa Tchiroma.

It is the latest in a series of cross-border raids carried out by Boko Haram, which have sparked a stronger international response in order to defeat the group.