P&O has said it is confident its takeover by Dubai Ports World will go ahead despite mounting opposition in the US.
The takeover of P&O's ports is causing concern in the US
Several US senators have warned they will oppose the $6.8bn (£3.9bn) deal over "national security concerns".
P&O controls six major ports in the US, including New York and Miami.
Meanwhile, a company based in the port of Miami has begun court action to prevent the takeover by DP World, which is backed by the Dubai government.
President Bush's administration has given its backing to the deal, which was agreed by the two firms last week, and has resisted calls from Congress to reconsider its stance.
But lawmakers from both the Democratic and Republican parties have questioned the takeover, and at least one Senate oversight hearing is planned for later this month.
Over the weekend, opponents of the deal voiced their concerns about whether security would be compromised by allowing a firm backed by a member of the United Arab Emirates (UAE) to takeover major US port operations.
The chairman of the House of Representatives Homeland Security Committee, Republican Senator Lindsey Graham, has called for an immediate freeze on the deal and demanded a "full and thorough investigation" of the sale.
He also dubbed the government's support of the deal "politically tone deaf".
Senator Chuck Schumer said: "The question that needs to be answered is whether or not they (Dubai) can be trusted to operate our ports in this post 9-11 world."
Assurances in place
But the US Government dismissed the concerns, saying it had given the deal a thorough review and had implemented the "appropriate" conditions and safeguards where necessary.
"We make sure there are assurances in place, in general, sufficient to satisfy us that the deal is appropriate from a national security standpoint," Homeland Security Secretary Michael Chertoff told ABC television.
However, he declined to give further details saying the information was classified.
DP World also shrugged off the claims saying security was "at the forefront" of its business.
Meanwhile P&O has insisted it has cleared all the correct regulatory channels after a partner in Miami filed a lawsuit to block the deal.
Eller & Company subsidiary Continental Stevedoring & Terminals launched the action late on Friday, saying that the sale was prohibited under its current agreement with P&O.
It argued that under the terms of sale it became an "involuntary partner" with Dubai and it may seek damages of $10m.
The takeover of P&O will make DP World one of the three largest container ports businesses in the world when it is finalised on 2 March.