"Ultimately the buck stops here," Dennis Hastert, leader of the Republicans in the lower house of congress, said at a news conference on Thursday.
However Hastert rejected calls for his resignation, despite coming under increasing pressure to reveal how much he knew about pornographic emails sent by the former Republican congressman Mark Foley to teenage congressional pages.
Some leading Republicans have publicly blamed Hastert for failing to take action as the scandal looks like to damage prospects in November 7's congressional election.
Hastert has said that he forced Foley to step down as soon as he became aware of his contacts with young pages.
However a former aide to the Florida congressman said he told Republican leaders of concerns over his conduct years earlier than they have acknowledged.
White House support
The White House has backed Hastert amid calls for his resignation saying "we support the speaker".
Foley resigned last Friday after ABC News reported that he had sent flirtatious emails to a teenage page. Since then, the broadcaster says, former Republican-sponsored pages have come forward with details of other lurid instant messages.
A committee will examine the
handling of the sex scandal
Congressional pages - who must be at least 16 years old - do low-level work such as running errands and answering telephones on Capitol Hill in exchange for an insight into the US political system.
The house of representatives' ethics committee has launched an investigation into the scandal and approved four dozen subpoenas for documents and testimony.
They will examine Foley's conduct and the handling of the scandal by Republican leaders.
Doc Hastings, the committee's chairman, said on Thursday that the investigation "will go wherever our evidence leads us". He refused to answer when he was asked if Hastert was among those subpoenaed.
Hastert welcomed the committee's actions and said he would instruct his attorney to co-operate with the panel "in getting to the bottom of this".
"The committee is moving to get control of this situation and find answers to provide all of us peace of mind," he said in a statement. "Any person who is found guilty of improper conduct involving sexual contact or communication with a page should immediately resign, be fired, or subjected to a vote of expulsion".