Tanzania's President Jakaya Kikwete has sharply criticised Kenya, Rwanda and Uganda for taking decisions at the East African Community without consulting other members.
"Do they want to create another community? Are they angry with our country or me, or do they want push us out?" Mr Kikwete said in parliament.
Nevertheless, he said Tanzania would not leave the EAC.
The speech is the latest sign of strained relations in East Africa.
Earlier this year, Mr Kikwete told Rwanda and Uganda to enter into talks with rebel groups battling them from the Democratic Republic of Congo.
The idea was dismissed by his Rwandan counterpart, leading to a diplomatic spat and rumours that the EAC was heading for disintegration.
Tanzania then sent troops to join a special UN brigade fighting another rebel group in DR Congo, the M23, which both Uganda and Rwanda are accused of backing. They deny the claims.
The EAC, which also includes Burundi, launched a common market in 2010 which allows for free movement of goods.
This year, Kenya, Rwanda and Uganda have held meetings at which they agreed on several joint projects , such as a new railway and speeding up the EAC's political union, starting with a common East African tourist visa for the three countries to come into effect in January.
"We hear that when some people are asked why Tanzania is not invited, they say: 'Tanzania would join later' - that this is a coalition of the willing. But we have never been invited," he told MPs in his speech, which was broadcast on national radio and TV.
"How could that be called a coalition of the willing?"
He dismissed claims he was being an obstacle to the development of the EAC.
He said Tanzania had always believed in strengthening the EAC and its institutions before embarking on a political federation - and benefitting economically was the main objective.
"If the economics are not OK, the community will be shaky. And we advise this from our own experience," he said, referring to Tanzania's union with Zanzibar.
The BBC's Basil Mbakile in Dar es Salaam says Tanzania has long been cautious about full economic integration with its neighbours, fearing its businesses make be swamped by stronger rivals in Kenya.
Although fast-tracking issues such as immigration, land, and employment were of particular concern, Tanzania would not abandon the EAC, the president said.
"We will do whatever we can to ensure that the community is not weakened or forced to collapse," he said.
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