Five suspects have appeared in court in the Kenyan capital Nairobi in connection with Tuesday's deadly hotel attack.

The siege, which lasted more than 18 hours and was claimed by the armed group, al-Shabab, left at least 21 people dead.

The court on Friday granted a request by the prosecution to hold the suspects - four Kenyans and a Canadian national - for 30 days in order to conclude their investigations.

"The team of investigators has so far covered considerable ground in the investigations," Noordin Haji, director of public prosecution, said in a statement on Friday.

"The investigations into this matter are complex and transnational and would, therefore, require sufficient time and resources to uncover the entire criminal syndicate," Haji added.

The suspects, identified as Joel Nganga, Oliver Muthee, Osman Ibrahim, Gladys Kaari and Guleid Abdihakim, were arrested on Wednesday in the Nairobi neighbourhoods of Eastleigh and Ruaraka, hours after the hotel siege ended.

George Kinoti, Kenya's director of criminal investigation, said on Wednesday those arrested were being treated as key suspects because they were in close contact with the attackers.

The al-Qaeda-linked group said it carried out the attack in response to US President Donald Trump's decision to recognise Jerusalem as the capital of Israel.

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Kenyan President Uhuru Kenyatta said on Wednesday all the gunmen behind the attack were killed, adding that Kenya will hunt down every individual that was involved in the siege.

On Friday morning, businesses in Nairobi's commercial hub of Eastleigh were closed in solidarity with victims of Tuesday's attack.

Traders told Al Jazeera the attack was an attempt by the armed group to hurt the city's business environment.

"We closed our businesses in solidarity with those affected by the attack. We are saddened by the situation in Nairobi," Abdi Mohamed Aden, a shopowner, told Al Jazeera. "They [the attackers] are trying to incite people against each other but that will not happen."

Mohamed Ali Abdi, a trader in the eastern suburb, said Tuesday's attack left people shaken but determined.

"We closed down our shops because we are mourning the death of our brothers, our fellow Kenyans who lost their lives. We want to tell those who want to destroy Kenya, we will destroy you," he said.

Of the victims of Tuesday's siege, 16 were Kenyan, one was British, one was American and three were of African descent but their nationalities had not yet been determined, according to police.

The attack at DusitD2 was the first in Nairobi since the Westgate mall attack in 2013, which left more than 60 dead.