TUNIS (Reuters) - Tunisia has deployed soldiers to stop a tide of illegal immigrants trying to reach Italy, a military source said on Monday, after Rome said a revolution in the north African country had set off a "biblical exodus." More than 4,000 migrants have crossed the sea from Tunisia to the small Italian island of Lampedusa in the past week, underscoring the lingering instability in Tunisia since protests ousted its president exactly a month ago. Some analysts believe revolts in Tunisia and Egypt could spread to other countries in the region, creating a potential nightmare scenario for European governments which have relied on autocratic leaders in north Africa to help curb migration. Catherine Ashton, the European Union's foreign policy chief, said on a visit to Tunis that she expected a trade deal with the bloc to be agreed within months, giving a boost to a Tunisian economy that has been battered by the turmoil of the past weeks. The flow of illegal migrants sparked a diplomatic row, with Tunisia accused Rome of infringing on its sovereignty after an Italian minister suggested sending police to Tunisia to stem the tide of people arriving on Lampedusa. "The military are controlling the coasts at Gabes and at Zarzis to stop the illegal migrants," the military source, who did not want to be named, told Reuters. "The military along with the coastguards are also present at the port of Gabes." The Gulf of Gabes is a favored launching point for the trip to Lampedusa - often made in overcrowded boats - while migrants were paying people smugglers $1,800 to cross from Zarzis, the International Organization for Migration said. Tunisian protesters unseated authoritarian ruler Zine al-Abidine Ben Ali on January 14, in an uprising that served as an inspiration for the revolt in Egypt which on Friday forced President Hosni Mubarak to resign. Since Ben Ali's departure Tunisia's interim government has been making faltering steps toward stability. But police have melted away in many places, and strikes and protests around the country are disrupting the economy. Speaking on Sunday, Italian Interior Minister Roberto Maroni, a member of the anti-immigrant Northern League, said the turmoil in Tunisia had triggered a "biblical exodus" to Lampedusa. "I will ask the Tunisian foreign minister for authorization so an Italian contingent can intervene to block the influx. The Tunisian system is collapsing," Maroni said on Italian television. The Tunisian foreign ministry said in a statement reported by the official media that it was surprised by Maroni's comments and that it "categorically rejects any interference in its internal affairs or any infringement of its sovereignty." Italian Foreign Minister Franco Frattini was scheduled to arrive in Tunis for talks on Monday evening. The EU foreign policy chief met Tunisia's interim prime minister, Mohamed Ghannouchi, and afterwards said the bloc planned to finish negotiations within months on granting Tunisia "advanced status" - which will mean preferential trade terms. She also said the EU planned to give Tunisia 258 million euros ($347.7 million) in aid by 2013, and would send election observers to help monitor the presidential election. "We would like to be Tunisia's main ally in moving toward democracy," she told a news conference. "We want to assist in the opening up and the democratic transition of the country."