NEW YORK-Two Muslim men, who are suspects in an alleged plot to detonate explosives in New Yorks subway system, face additional charges, federal prosecutors said on Thursday. Zarein Ahmedzay, who is of Afghan origin, and Adis Medunjanin, a Bosnian American, face charges of conspiracy to use weapons of mass destruction against persons or property in the US and several other charges, federal prosecutors said in a statement. They had faced lesser charges. Prosecutors say Ahmedzay and Medunjanin 25-year-old US citizens and residents of the Queens borough of New York conspired with Najibullah Zazi 'to attack the New York subway system in mid-September 2009. Zazi pleaded guilty this week to conspiring with others to blow up New York subway targets with homemade bombs. A federal grand jury issued a new indictment charging Ahmedzay and Medunjanin on charges of conspiracy to commit murder in a foreign country, providing material support to a foreign terrorist organisation al Qaeda-and receiving military-type training from al Qaeda, prosecutors said in a statement on Thursday. Ahmedzay also faces a charge of making false statements to the FBI, the statement added. Both men pleaded not guilty in Federal court on Thursday. Jeffrey Knox, an assistant US Attorney, said that additional charges are likely and that 'additional defendants are likely from overseas. Knox also gave more details about the alleged plot, saying that the suspects planned three coordinated bomb attacks on the Manhattan subway during rush hour. Two of the four charges that both men face-conspiracy to use weapons of mass destruction and conspiracy to commit murder in a foreign country carry a maximum sentence of life in prison. They face up to 15 years in prison if convicted of providing material support to a foreign terrorist organisation. The maximum penalty is 10 years in prison for receiving military-type training from al Qaeda. The two men were indicted last month and pleaded not guilty. The charges that federal prosecutors detailed Thursday come from a fresh indictment that supersedes, or replaces, the original charges. Ahmedzay worked as a taxi driver while Medunjanin was employed as a building manager. Both were friends with Zazi, who is of Afghan extraction. He lived in Colorado. Zazi pleaded guilty this week to conspiring to use weapons of mass destruction, conspiracy to commit murder in a foreign country and providing material support to a terrorist organization. 'In spring 2008, I conspired with others to join the Taliban, to fight alongwith the Taliban against the United States, he said in court Monday. 'We were recruited to al Qaeda instead. The threat of legal action against Zazis associates and family played a role in his decision to cooperate with the government, according to CNN, citing a law-enforcement source. The source said Zazis parents faced potential immigration fraud charges. They were not facing deportation but did face the possibility of criminal penalties. Zazis father, Muhammad Wali Zazi, initially was charged with lying to investigators, but in January a federal grand jury in New York charged him with conspiracy to obstruct justice by helping to discard bomb-making chemicals when he learned of the governments investigation. A judge is scheduled to sentence Zazi June 25. He faces a maximum sentence of life in prison for the first two counts and an additional 15 years in prison for the third count, the Justice Department said in a statement.