The African Union has asked the United Nations Security Council to back a naval and air blockade of Somalia.
A blockade would stop piracy and the flow of arms reaching insurgent groups fighting the transitional government, said Ramtane Lamamra, AU commissioner for peace and security.
He also repeated a call for international troop numbers to be increased from under 8,000 to 20,000.
Somalia's fragile government is battling an Islamist insurgency.
The al-Shabab militia - which now controls much of southern and central Somalia, including parts of the capital, Mogadishu - is linked to al-Qaeda.
However, the government, backed by AU troops, has recently gained some ground.
"The African Union is very concerned that the insecurity in Somalia is spilling over into the region," Mr Lamamra told the UN Security Council.
He called on the council to authorise a force of up to 20,000 troops and nearly 2,000 police.
Crucially, he urged the UN to make sure they had enough money and resources, says the BBC's Barbara Plett at the UN in New York. Fewer than 8,000 soldiers have been deployed so far and they are badly paid and equipped, she adds.
The calls for both the blockade and extra troops were backed by Somalia's UN-backed government.
"At this point now it's an open no-man's land. Anything goes in and out," Somalia's ambassador to the UN Omar Jammal told the BBC's World Today programme.
Security Council president Ruhakana Rugunda said the requests were "legitimate" but would need to be studied further.
Mr Rugunda is UN ambassador for Uganda, which supplies the bulk of the troops already in the AU force in Somalia (Amisom).
Uganda is pressing the case for enlarging the force, our correspondent says.
However, other countries - such as the UK and France - are more wary of funding missions over which the council has limited control.
Mr Lamamra criticised the UN's policy as limited engagement and half-hearted measures, and urged an increased effort to confront the threat posed by Somalia to regional and international security.
In July, al-Shabab said it carried out two bombings in the Ugandan capital, Kampala, in which at least 76 people were killed, in revenge for the presence of Ugandan troops in Mogadishu.