Sudan's President Omar al-Bashir is visiting neighbouring Chad, in defiance of calls from the International Criminal Court (ICC) for his arrest.
The trip is the first time Mr Bashir has set foot on the soil of a court member since the ICC called for his arrest on war crimes charges in 2009.
Chadian officials said Mr Bashir, who denies the charges, would not be arrested.
Chad and Sudan have often clashed bitterly over the Darfur conflict.
According to the rules of the ICC, which has no police force and relies on member states to make arrests, Chadian forces are required to arrest Mr Bashir during his stay in the country.
Earlier this month, the ICC added genocide to the charges against Mr Bashir.
But the Sudanese president seemed more focused on improvements in relations between the two neighbours than on the possibility of his incarceration.
"Chad and Sudan had a problem in the past. Now this problem is solved. We are brothers," the Associated Press news agency reported him as saying.
During the conflict in Darfur, rebel groups based in both countries have launched attacks on their rivals from behind the sanctuary of their own borders.
Khartoum accused Chad and its President Idriss Deby of supporting anti-government rebels in Darfur.
In turn, Chad insisted that Sudan was backing rebels attempting to overthrow Mr Deby.
However, the two presidents met earlier in 2010 for the first time in six years, announcing they were ready for a full normalisation of ties.
Despite the issue of the ICC charges against Mr Bashir, the international community is pleased the two countries are now getting on, reports the BBC's East Africa correspondent Will Ross, because it potentially increases the chances of ending the long-running conflict in Darfur.
Mr Bashir is visiting Chad to attend a meeting of the Community of Sahel-Saharan States (Censad), of which Sudan is a member. It is his first visit to a full ICC member state since his indictment in 2009.
But there was little concern among officials that the visit to N'Djamena would be disrupted.
"Bashir will not be arrested in Chad," said Chad's Interior Minister Ahmat Mahamat Bachir.
One Sudanese official told Reuters news agency before leaving Sudan: "If there was 1% of a doubt about Deby, we would never let Bashir go."
Even before he arrived, rights organisations condemned the decision to allow Mr Bashir into the country.
"Chad risks the shameful distinction of being the first ICC member state to harbour a suspected war criminal from the court," said Elise Keppler of Human Rights Watch.
"Chad should not flout its obligations to arrest Bashir if he enters Chad."
The next decision for Mr Bashir is whether to attend this weekend's African Union summit in Uganda, our correspondent says.
The African Union has said it will not honour the ICC warrants, but like Chad, Uganda is a signatory of the court.
But relations between those two countries have blown hot and cold so often, the Sudanese president may well decide not to ride his luck and instead head home, our correspondent says.
Child soldiers deal
The Chad-Sudan rapprochement comes shortly after one of Darfur's leading rebel groups announced that it had signed an agreement to allow the UN access to its bases to check children are not being recruited as soldiers.
Jem leaders, who travelled to Geneva for the signing, said the movement had no child soldiers but agreed to it as a gesture of goodwill.
Fighting intensified in Darfur in May after Jem pulled out of peace talks with the government, accusing it of acting in bad faith.
The UN estimates the conflict in Darfur has cost the lives of 300,000 people and driven a further 2.7m from their homes.
The government puts the death toll at 10,000 and has said the problems in Darfur have been exaggerated for political reasons.