NAIROBI, Kenya—Sudan's president, who faces charges of genocide in connection with massacres in Darfur, attended the signing of Kenya's new constitution Friday at the invitation of the government here, deepening tensions between this East African nation and the International Criminal Court.

The court has issued an arrest warrant for Sudanese President Omar al-Bashir. As a signatory of the treaty establishing the international court, Kenya is required to take Mr. Bashir into custody and turn him over to the Netherlands-based court to stand trial.

But on Friday, President Bashir sat with other dignitaries and heads of state at a ceremony celebrating the adoption of a new Kenyan constitution that aims to curb corruption, impose new checks on executive power and reduce ethnic tensions.

Clad in a dark suit, Mr. Bashir joined in releasing white doves—symbols of peace—to mark the occasion.

Political analysts said Kenya's welcome of Mr. Bashir at such a pivotal time is a sign of Nairobi's desire to bolster ties with Sudan, Africa's largest country and one with which Kenya shares a border. It is also intended to serve as a pointed message to Western powers that it won't be pushed around.

Kenyan leaders are "saying they're an independent country and that they're going to play hardball," said Ben Rawlence, a researcher for Human Rights Watch, a U.S.-based advocacy group. "This is a big slap in the face, a big step backwards for everything they've said they stand for."

Kenya's decision to welcome Mr. Bashir comes as the International Criminal Court is expected to issue arrest warrants for Kenyan officials allegedly involved in 2008 postelection violence here. Kenyan President Mwai Kibaki and Prime Minister Raila Odinga have said they will cooperate with the court.

The foreign ministry spokeswoman, Judith Ngunia, said Kenya was adhering to a recent directive by the African Union that its members should not arrest Mr. Bashir. "We are members of the AU too," she said. A Kenya government spokesman didn't answer calls to his cellphone Friday.

The African Union, a group of African nations, recently voted to ignore the arrest warrant for Mr. Bashir because it fears a contentious war crimes trial could interfere with efforts to heal the rift between the north of the country and its autonomous south and resolve the conflict in the Darfur region.

But some AU members, including South Africa and Botswana, have said they will arrest the Sudanese president if he attempts to enter their countries.

Kenya's decision to invite Mr. Bashir to Nairobi could strain the country's relations with Western donors. The U.S. and European nations have said that Mr. Bashir should appear before the International Criminal Court.

On Friday, the panel of three judges handling Mr. Bashir's case released a statement noting that Kenya "has a clear obligation to cooperate with the Court." The judges said they would immediately inform the United Nations Security Council "in order for them to take any measure they may deem appropriate." The court cannot force states to comply with its directives.

Mr. Bashir served as president of Sudan while militias backed by his government killed an estimated 200,000 people in Darfur, a region in the northwestern part of the country, after attacks by antigovernment rebels there.

The Sudanese leader has declined to appear before the International Criminal Court. In April, he was re-elected president in a general election, paving the way for a referendum to be held Jan. 9 to allow the now autonomous southern region of Sudan to determine whether it wants to become independent. It is expected to vote to secede.